Historical Accuracy and Period Correctness - and they enjoy the stench of rotten eggs. Is my guess. I used Pyrodex for a spell back in the late 1980's, when real black became near impossible to find locally. (the Internet had not been invented at the time, and I did not have a computer, anyway.) It shot well enough in the CVA rifles and (steel framed) reproduction revolvers I had back then. I think I currently have two pounds of FFg Swiss, and around a half pound of RS Pyrodex in reserve.