Red Bear,, it has to do with ammo costs & availability.
The 38 spl was a very popular caliber,, especially among LEO's for decades. As such,,, ammo was cheap & available. And the 357 was the easiest to find & it can shoot both calibers.
The 45 Colt & 45 acp,, with the Colt being very limited in factory offerings, not always available,, yet a heck of a great caliber when reloaded in modern firearms,, it is popular. But expense of Colt ammo makes it less than desirable to the non-reloader. BUT, when you add a 45 acp cylinder,, combined with the fact that for many decades the 45 acp was the military caliber,, it's ammo availability & cost made that convertible very popular.
But the OP was about the 10mm/40 S&W. And again,, find a wide variety of factory offerings in 41 mag,, & look at what's available AND the expense. Now,, reloaders,, even finding brass isn't as easy as we'd like.
BUT,,,, the 40 S&W is a popular LEO caliber,, so ammo & brass is very cheap. The 10mm is kinda like the 41 mag in that it just won't die because it can do a lot & is appreciated.
Throw in the fact that a lot of modern shooters prefer semi-auto action designs,, so to allow those of us who like revolvers the option,, they build revolvers in it. As a reloader & a revolver person,, we have it made. We can find brass AND ammo cheaply,, auto guys often lose brass or don't pick it up. Heck,, at my range the last 2 USPSA matches,, a guy was using a 10mm & I got close to 250 pieces of 10mm brass just for the time it took to pick them up!
Don't get me wrong,, I do enjoy & appreciate the 41 mag. In fact,, I have more of them than I do 40's & 10's combined. BUT, as a guy who understands the general public casual shooter types,, it's hard to find AND afford good top quality 41 mag ammo in many stores. So, casual Joe,, non-reloader,, who wants to feed his semi-auto,,, can easily go to the local discount store, & buy cheap ammo to blast with. While the dedicated types,, who enjoy revolvers,, appreciate the versatility of a convertible caliber firearm,, and reload,,, can get the most out of the calibers. And it's easy to see that the manufacturers see the same things,, as these guns are selling & desirable. So,, many of us who enjoy versatility,, appreciate the fact we have options.
And besides,, why limit yourself to just one caliber or one gun?
The 41 mag to me,, is a heck of a great caliber. When properly loaded,, it makes an excellent hunting round,, or it can be a superb target gun with less felt recoil to most than the 44 mag & others.
So, the short answer is ammo availability & costs.