I think the military higher ups felt ammunition was a valuable resource that should not be wasted so they favored slow, deliberate fire. Case in point: the Little Bighorn in 1876. Many of the NDN's had repeating, lever action cabines while the Army had the single shot, trap door Springfields. I think I read that when the Spencer was brought out Lincoln himself tested it and immediately wanted them made for the mounted troops. He obviously saw the advantage.
This slow, aimed fire continued through WWI, I don't think it was until the Garand and WWII that the military started changing its mind about fire power.