I think the whole idea behind the cartridges Colt and others offered was to make money by providing something that would be of great convenience to the people who bought his pistols.
Most of them were plain people who wanted a pistol to defend themselves and their homes. They weren't avid gun lovers who owned a lot of guns so most of them didn't have any powder around the house or balls or bullets or the means of making them.
These people, just like the millions of people today weren't interested in buying bullet molds and doing all the things we, few, muzzleloaders love. They just wanted something that they could use that was simple and handy and easy to use and they found that Colt was more than happy to supply exactly what they wanted, for a fee.