My takeaway, in a historic sense, was that, during the battle, the Indians were using Winchester lever actions, which didn't jam, as readily, as the trap door rifles. In the heat of battle, this gave the Indians a considerable advantage.
This particular battle wasn't an accidental win for the Indians. Chiefs Crazy Horse, Sitting Bull, Gall, and a few others were disgusted and angered, by Custer's savage, indiscriminate, and treacherous abuse of power, and military authority, against encampments of women, children and the elderly. Their response was this well co-ordinated attack.
As to battlefield pickups, many Indians must have recognized the trap-door, while not a great choice for a combat weapon, was still very usable as a hunting rifle. But I imagine the Colt revolvers were as valued then, as they are today, and being far easier to ruck, were a first choice of spoils, among the victors.