The .50-70 was never really seen as anything more than a stop-gap cartridge while a newer, smaller caliber round was developed.
As originally adopted, the .45-70 had a 405-gr. bullet. It was ballistically superior to the 450-gr. bullet of the .50.
The .45-70 with the 500-gr. bullet wasn't adopted until 1879, when testing at the Sea Girt grange showed that it was a lot better at long range.
And, a little known tidbit about the Span-Am war...
Regular Army troops were issued the then standard Krag Jorgenson rifle.
Volunteer troops were all issued Trapdoors in .45-70.
Except for one unit.
Teddy Roosevelt apparently pulled some strings as former Ass't Secretary of the Navy and got the Rough Riders Krags.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.