Believe it or not 'repeaters' did exist back then. The problem was that ammo wasn't cheap to mass produce. Plus government being government at the time.

Lincoln even considered using repeaters during the Civil War but was talked out of it by aides who said they couldn't waste precious ammo.

Many cavalry units used the breach loading Sharp’s carbines, but muskets were standard issue because there were more available in warehouses. Armies were actually slow to adopt new firearm technology and civilians developed most of it.