I'll use myself as an example, regarding the 10mm.
I know that the .45 Colt is a proven performer, and of course, all those calibers above it. But I don't want, for valid reasons that are not uncommon, to carry a large frame revolver - and maybe I just want to carry an auto if possible anyway - one that at doesn't require modification or for me to take on the role of crash test dummy. At this time (unlike ten or more years ago), I can walk into several local gun stores and find on the shelf, factory loads in 10mm that surpass any 45acp loads there by a measurable (I would say significant) degree. While I may be aware that it's possible that I could accomplish what I want (deep penetration on large animals) with one or more of the 45acp+p loads that I might find, it is arguable that the 10mm loads I can readily find in stock will penetrate better (higher velocity + SD per weight), and will certainly not penetrate less.
Having no such experience killing large animals with handgun calibers, which one do you think I might gravitate to, especially if already wanting to buy a new gun? Not another 45acp. I'd propose that I am not even close to unique in that regard, and that is why the 10mm is probably not going away this time, unless some outside factor is inserted.
As you might deduce, this can have a snowballing effect. As more varied and effective loads become available, more gun buyers may decide to go with 10mm, which should motivate ammo makers to provide more 10mm ammo....and on it goes. Until somebody convinces us that the 10mm is somehow a mistake, or something better and more viable comes along. For a while, everybody thought that was the 40S&W, but now, not so much. I don't see that happening again soon, but I could be wrong.
