The idea of using a revolving cylinder to have more loaded shots available dates way back.
The idea of mechanically indexing that rotation took some time, and some large improvements in machining to materialize.
The idea of having the axis of rotation paralleling the bore was not universal, either. There were a number of "turret" designs out there, both horizontal and vertical. (Mind, having loaded cylinders facing the firer did give some pause, as chain fires were a thing in those days before machined powder became common.)
Sam Colt had the benefit of a number of innovations coming together at just the right time.