I've heard a bunch of stupid arguments when I asked them that. But imo they don't switch because they're used to it and cba learning a new game with 100+ heroes and all the shit that comes with it.
From what I know, you can progress your account with a real effect on it, like you become more powerful or something.
They just don't want to play without their compensation crutch, whatever it is.

I'll have to check that game too, see what is all the fuss about it.