The loyalty you see in calibers and guns has to do with a view point. If a person only looked at guns and calibers that were practical for self defense and home defense, then they would pretty much be looking at 357 magnum revolvers only. They have the reliability and dependability over a semi-auto. It also can take care of shooting any level of power and recoil that the shooter wants. From low end 38 specials, to 38 +P, to weak 357, to the most powerful 357 magnum.
There is absolutely no need for a 17 round magazine. For civilian self defense purposes, a 6 shot revolver or 7-8 shoot magazine is more than enough. For the person who practices a lot and a revolver just isn't practical or desired, there are a number of semi-autos available. I have large hands, so carrying a revolver is not very comfortable. I can't really shoot a "J" frame or smaller. The only real comfortable guns are "K" frame and larger. So instead, I go with semi-autos. Obviously not mouse guns. But one of the reasons for the "Caliber Loyalty" is because of Hollywood. But this isn't something new. Growing up as kids, we were impressed with the 45 long colt of the cowboys and indians. Well there's a lot of people who like the Die Hard, lethal weapon, and terminator type movies. They see cops shooting high capacity magazines which usually means the 9mm or 40sw and they think they need them. "If it's good enough for hollywood, it's good enough for us".
Then there's the historical/military crowd that likes a certain caliber because of it's past. That's one reason for getting an M1 Garand, loving 1911A1, Winchester 30-30 lever actions, etc... There's a lot of reasons for caliber loyalty.
I do wish people would learn to pick the right gun for them, and not basing it on the caliber or gun that someone suggested to them. Suggesting a manufacturer is good. You're promoting a company's quality, service, etc... I.e For revolvers, I ALWAYS recommend S&W or Ruger. That's it. They are the best. For semi-autos, I suggest SigSauer,Colt, Springfield, and certain other brands. But I NEVER suggest a caliber. For some people or under certain circumstances, the 25 or 32acp is the RIGHT CALIBER. For some people, it's the 9mm. For some it's the 45acp. And it's NOT BECAUSE of the caliber. It's because of the gun. The gun was the right fit for the person. The caliber doesn't matter at all. If the gun that fits me perfect, feels good shooting it, lets me carry it and feed it comfortably; then it's a good choice for me. It doesn't matter if it's a 32, 9mm, 357 mag, 40, 10mm, 45acp, or 44 mag. And round capacity is definitely NOT a factor. We aren't police, military, swat, etc... We aren't fighting gangs, breaking into drug houses, shooting through walls, doors, and cars.
Anyway, there's a lot of reasons for caliber loyalty. Some are some decent reasons. Some are hollywood.