Well, none of us is Claud E. Fuller, after all...even if such a collection as his was possible today even Fuller "concentrated" on the US 1861 with all of the various contractor made specimens. Clearly he was fond of American model military arms, including CS models but specifically there was something about the US 1861 that appealed to his individual preferences. More guys today seem to be Enfield P53 enthusiasts than US 1861. I don't know why that is. Whatever the case, if there is something about a particular arm that appeals to your eye, then there doesn't need to be a better reason than that.
Oddly, I am not a Civil War arms collector. The only historical long arm of any era on display at all in my house? An American mountain rifle in flint that I built from a kit many years ago. It is nothing fancy but it took me a very long time to get it "just right" to my eye and set up the way I wanted it to be when I shot it, the lock timing, etc. And I feel good about it every day when I look at it perched up there. One does not "buy and sell" an old friend...