The thing is that it's basically a contest of morale and hesitation.
A cavalryman with a battle trained horse can expect the horse to charge directly at infantry up to the last few yards, but a cavalryman with a conventional (not battle trained) horse will expect the hose to have rather more sense and so need to control the horse quite a lot better.
Meanwhile, a perfectly executed cavalry attack can achieve success if only a few infantrymen waver, but a cavalry attack collapses if the cavalrymen waver even if the infantymen waver as well.
And while I'm at it, a properly executed attack by cavalry doesn't involve a thousand cavalry - it involves two lines abreast. The second is there to fill in the holes caused by casualties in the first, but there's no point having a third line, and that means an attack by a thousand cavalry at once is equivlaent to the frontage of 25 infantry squares - you can't possibly see most of it - and it's not the best use of the cav anyway. The extra numbers is useful mostly in allowing repeated attacks and exploitation.
Making this work, of course, involves drill. And it's complex drill, while the fundamentals of operating in square can be taught in a very short time; Minty knew what he was about as he'd had experience in an army which used shock cavalry, and it took quite a long time to promulgate that skill.
I understand what you are saying here but ... times were a changing.
Military men were waging theoretical battles over the role of cavalry and the impact of the new weapons on tactical usage throughout the period from the 1850s up to WWI. The school of
la arme blanche fought furiously with the "mounted infantry" advocates in every military journal of the day. The eventual most-world-famous expert on the use of Cavalry ends up being a Canadian Lt. Colonel named George T. Denison (in 1877, won the word-wide competition for the prize offered by the Grand Duke Nicholas, Inspector-General of the Russian Imperial Cavalry, in 1875); he remained at the top up until WWI and his work is considered essential to anyone studying the use of Cavalry. Denison's 1877
History of Modern Cavalry is cited by Heinz Guderian in his 1937
Acthung - Panzer! (Guderian thought Denison was a visionary far ahead of his time).
The changes in technology made definite changes in the practicality of the common techniques used on the battlefield. The improved reliability, range and accuracy of fire weapons reduced the effectiveness of old-style shock combat methods. Battlefield saber charges by large mass groups of cavalry became harder to manage and successfully execute. Cavalry casualties when exposed to firepower soared.
In his pre-Franco-Prussian War
1869 Instructions to Large Unit Commanders, Helmuth von Moltke stresses how the rise of battlefield firepower has impacted the use of cavalry, making them much more vulnerable and dependent for battlefield success on preparation by the other arms. He cautions his generals on leaving cavalry where they will be unnecessarily exposed to infantry and artillery fire, while still wanting them held close to the front for quick exploitation of battlefield opportunities (an early version of Catch-22, I guess). Von Moltke has been preaching about the supremacy of firepower on the battlefield since he observed the French fighting the Italians in 1859 in Italy; the 1866 Austro-Prussian War experience simply reinforced those lessons in his mind. He still wanted the traditional Cavalry role of mobility and exploitation, but acknowledged that firepower made the cavalry more vulnerable and fragile.
Famed British historian and teacher G. F. R. Henderson toured many Civil War battlefields in Virginia, knew many Confederate generals, and thought that the terrain was clearly unsuited to mass cavalry actions (he also toured many European battlefields of the 1800s and found them much more open and suited to cavalry). A decorated veteran, he later was Kitchener's aide in the Boer War, a major factor in the British victory there, and came away with an even greater respect for the impact of rifle fire on exposed troops. He was more of a "mounted rifles" man, although the British Army was violently split on the
la arme blanche/"mounted Rifles" issue, particularly in the period from the Franco-Prussian War to the Boer War.
A few years after the Civil War, Phil Sheridan was an observer at the Battle of Gravelotte in the Franco-Prussian War. Here is an account he gives of a cavalry charge he witnessed there:
But it was now time for the German right to move in earnest to carry the Rozerieulles ridge, on which crest the French had evidently decided to make an obstinate fight to cover their withdrawal to Metz. As the Germans moved to the attack here, the French fire became heavy and destructive, so much so, indeed, as to cause General Von Steinmetz to order some cavalry belonging to the right wing to make a charge. Crossing the ravine before described, this body of horse swept up the slope beyond, the front ranks urged forward by the momentum from behind. The French were posted along a sunken road, behind stone walls and houses, and as the German cavalry neared these obstructions it received a dreadful fire without the least chance of returning it, though still pushed on till the front ranks were crowded into the deep cut of the road. Here the slaughter was terrible, for the horsemen could make no further headway; and because of the blockade behind, of dead and wounded men and animals, an orderly retreat was impossible, and disaster inevitable.
About the time the charge was ordered, the phase of the battle was such that the King concluded to move his headquarters into the village of Gravelotte; and just after getting there, we first learned fully of the disastrous result of the charge which had been entered upon with such spirit; and so much indignation was expressed against Steinmetz, who, it was claimed, had made an unnecessary sacrifice of his cavalry, that I thought he would be relieved on the spot; though this was not done. Followed by a large staff, General Steinmetz appeared in the village presently, and approached the King. When near, he bowed with great respect, and I then saw that he was a very old man, though his soldierly figure, bronzed face, and short-cropped hair gave some evidence of vigor still. When the King spoke to him I was not close enough to learn what was said ; but his Majesty's manner was expressive of kindly feeling, and the fact that in a few moments the veteran general returned to the command of his troops, indicated that, for the present at least, his fault had been overlooked.
On the next day, Sheridan passed over that ground:
Breakfast over, the Chancellor invited me to accompany him in a ride to the battle-field, and I gladly accepted, as I very much desired to pass over the ground in front of Gravelotte, particularly so to see whether the Krupp guns had really done the execution that was claimed for them by the German artillery officers. Going directly through the village of Gravelotte, following the causeway over which the German cavalry had passed to make its courageous but futile charge, we soon reached the ground where the fighting had been the most severe. Here the field was literally covered with evidences of the terrible strife, the dead and wounded strewn thick on every side.
In the sunken road the carnage had been awful; men and horses having been slaughtered there by hundreds, helpless before the murderous fire delivered from behind a high stone wall impracticable to mounted troops. The sight was sickening to an extreme, and we were not slow to direct our course elsewhere, going up the glacis toward the French line, the open ground over which we crossed being covered with thousands of helmets, that had been thrown off by the Germans during the fight and were still dotting the field, though details of soldiers from the organizations which had been engaged here were about to begin to gather up their abandoned headgear.
Later, near Sedan, Sheridan witnessed another cavalry action:
After a severe fight, the Crown Prince drove the French through Floing, and as the ground between this village and Sedan is an undulating, open plain, everywhere visible, there was then offered a rare opportunity for seeing the final conflict preceding the surrender. Presently up out of the little valley where Floing is located came the Germans, deploying just on the rim of the plateau a very heavy skirmish-line, supported by a line of battle at close distance. When these skirmishers appeared, the French infantry had withdrawn within its intrenched lines, but a strong body of their cavalry, already formed in a depression to the right of the Floing road, now rode at the Germans in gallant style, going clear through the dispersed skirmishers to the main line of battle. Here the slaughter of the French was awful, for in addition to the deadly volleys from the solid battalions of their enemies, the skirmishers, who had rallied in knots at advantageous places, were now delivering a severe and effective fire. The gallant horsemen, therefore, had to retire precipitately, but re-forming in the depression, they again undertook the hopeless task of breaking the German infantry, making in all four successive charges. Their ardor and pluck were of no avail, however, for the Germans, growing stronger every minute by the accession of troops from Floing, met the fourth attack in such large force that, even before coming in contact with their adversaries, the French broke and retreated to the protection of the intrenchments, where, from the beginning of the combat, had been lying plenty of idle infantry, some of which at least, it seemed plain to me, ought to have been thrown into the fight. This action was the last one of consequence around Sedan, for, though with the contraction of the German lines their batteries kept cannonading more or less, and the rattle of musketry continued to be heard here and there, yet the hard fighting of the day practically ended on the plateau of Floing.
Sorry to be so long. The point is not that a successful cavalry charge against infantry had become impossible. The point is that a successful cavalry charge against infantry had become more difficult and perilous, making it a bad choice in more and more situations.
This is the result of development of new technology, starting with the percussion cap and progressing through the Minie rifle to the bolt-action rifle, to include rifled artillery and the introduction of the Krupp breech-loading artillery by the time of the Franco-Prussian War. It is the
mass deployment of these weapons that causes the impact to be effective. Repeaters and magazine-rifles, machine-guns, etc. increase the impact, but before they are deployed to the mass of the armies fighting their impact will always be erratic and minimized by their scarcity. (This is why you can find specific examples of how repeaters made a big impact in particular parts of battles in the Civil War -- but also why they did not have a large impact of the war as a whole: they were used by only a small part of the troops fighting.)
Trivia: I have a friend, third-generation West Point on both sides of his family, who had a grandfather serving with the 26th US Cavalry in the Philippines in 1941. The other day I saw a post from him featuring a painting of the regiment's mounted charge at Morong, the last in US history, during the retreat to Bataan.
In the painting, the troopers of the 26th seem to be using .45 automatics. His grandfather on that side was on Corrigedor by then, survived the Death March, but was killed when US planes sunk a ship transporting POWs to Japan in 1944; the grandfather on the other side was with a Tank Destroyer unit at Kasserine Pass in 1943 and finished the war invading the south of France and coming up into Germany. His father served in Vietnam. My friend did his service in Germany, IIRR, and is a bit of a cavalry nut.:Ghost: