Well rifles are easier to go to and from.
Look at the simple NATO 308 case and you have the 243, 7-08, 308, 338, 358 Win. And the reason ot neck up or down is to get differant proformance out of an action to launch larger or smaller bullets in both weight and caliber. And depending on the game you are hunting and the terain.
Now look at the Nato 9X19 and you do not have people necking it down.
With most of the strait wall hand gun calibers can not be necked up (well the 50 AE will prove me wrong as they blew out the 44 mag case ot make it)
But you really only have a few purposes for a handgun.
Personal protection, target, and hunting.
There are many different platforms for but only a few calibers have stood the test of time.
there are a few that are hanging on with a cult following.
You now have a a few nitch market guns like the BFR that shoots 22 hornet to 450 marlin and most lever rounds inbetween
you have the T/C contender market for the really odd ball wild cat rounds.
You also have the forign military guns for strange calibers. 8mm nambu, 30 mauser, 9mm Largo, 455 Webley, 9mm Galistini.
But you look at the balistics of many of the pistol rounds and many over lap.
If 9mm X19 gives you 350 Ft pounds it is a 355 dia bullet would you spend more for a 36 caliber bullet that gives you 360 foot pounds?
And while some calibers over lap a lot of the difference is the size of the platform.