For me, caliber choice is just as personal as it gets. But keeping up with trends has never been my deal. At least since I grew up a little and figured it out, kinda. It's always been out of necessity, really with every gun I've ever owned. (With the exception of one Colt Delta Elite 1911 10MM back in the late 80's) and that ironically it was enough to turn me off to 10MM. I'm sure technology has made them far more shootable but still. No 10mm for me thanks. That Colt broke me from 10s a looong time ago. It's the only gun I've taken a huge hit on as far as resell, just to get rid of it. So I am not a fan from a bad personal experience. And I can safely say, it was the worst gun I've ever owned.
But that's just me and my experience. It's all about PERSONAL preference and what works best for the job at hand. Like any other tool.
I've had to drop from a .40 to a 9mm. Out of necessity. That being said, that's always been my driving factor. The recoil, form the .40 hits a nerve just right in my shoulder, and can cause me to lose my grip, I've nearly dropped mine from pushing past my limit. No bueno! I can shoot better, train longer, etc. with a less snappy 9mm pistol, that I can control the most effectively. I changed from .45 to .40 cal iirc in '96-'97 and I never looked back. Until about a year ago. And I've gone to a 9mm for the first time, I am so much better with it than the lager calibers, and it's more enjoyable to train now.
I have no idea why "caliber trends" do what they do. It's a debate that's probably as old as guns themselves. But, for as long as I can remember, the FBI has set the standard, for what people consider the "best" most effective round in general. And our civilian reaction to what their "best round" seems to repeat itself. My biggest guess would be just that, and secondly reloading is big for some.
Bottom line is, there is no "best round" for EVERY situation.
My unsolicited advice is to find what you can be the most effective with, then train, train and train some more with it. End of story. Period.