I think we're guilty sometimes of applying modern day preferences and ideas to the 19th century. Today, most of us have no experience with the .44-40 or .38-40 but the .45 Colt is very well known. We may be imagining that it was like that in the 1870s and 1880s, too, but it wasn't. Moreover, the Colt Single Action Army revolver did not sell in huge numbers before WWII and probably only about half the production was in .45 Colt and most of those going to the army (Sorry, don't carry the numbers around with me). Other, smaller revolvers outsold the larger ones and always had. To an extent, that was also true of the .45-70.
So basically, the .45 Colt chambering was not necessarily something that a gunmaker just had to have because no one wanted anything else.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.