Hmm, an eternal question. But what if the Federal gov't was impeded from providing the now complained about protection by the state of Texas itself?
From page 79 of a thesis entitled,
States Rights in Texas: The Growth of an Idea, 1850-1860
While the federal government was unquestionably sincere in its efforts to safeguard the frontier, its policies, from the beginning, were constantly criticized by Texans. Many were the weaknesses of the federal In¬ dian policy and none went unnoticed. First, the military force was inadequate to afford protection. Scattered over hundreds of miles, the unmounted soldiers had little opportunity to encounter Indians on horseback.
Second, because Texas was a state rather than a territory, the army and the federal Indian agents had less authority than they otherwise would have possessed. To regulate intercourse among citizens, traders, and Indians was the state's function; Texas, however in the late 1850's was unable to do this. Still the state would not give *the federal agents or the army unlimited power to handle the problem.27
Third, frontier defense was an expensive undertaking. Sam Houston charged in 1852 that the national government was spending .$6,000,000 & year to preserve the Indian peace; that the sum was uselessly ex¬ pended; and that, given $100,000, he could guarantee peace on the frontier.When the inefficiency of the federal troops (especially after 1856) forced Texas to summon its Rangers to defend the frontier, the state naturally expected to be reimbursed by the federal govern¬ ment . That it was not only intensified the criticism of that government.29
27 See Webb, Texas Rangers,pg. 128.
28 See Clarence R. Wharton, Texas Under Many Flags (5 vols., Chicago, 1930), II, 3
But, it appears that the Texans, in conflict with a Federal policy of peaceful coexistence, were more interested in Indian extermination and were forced to rely upon the valiant Texas Rangers.
Those weaknesses in governmental policy were significant, but it was the government's attitude towards the Indians which provoked greater condemnation. Essentially the federal government strove to protect the Indians against extermination as long as they were peaceful. The Texans, however, impatient with the clumsy methods and humanitarian policy of the United States army, believed that the federal government should enroll the Rangers, pay them, then allow them to !,run all the Mexicans into the Rio Grande and all the Indians into the Red River."3°
https://scholarship.rice.edu/bitstream/handle/1911/89083/RICE0120.pdf?sequence=1
This to appears to be less than a failure of protection than a straight out advocacy by the state of Texas of a policy of extermination. But, I suppose if Texans WERE DEMANDING IT, then it must be OK.