Because majority of private servers actually monitor their game and prevent/ban use of exploits on their server.
Q lock has a rich history of exploits and abuses attached to it so the majority if not all private pvp servers abandoned it altogether.
As you said yourself CE is not a new game so privates have a specific “core player base” who like or adjusted to those settings over the years.
Also, you’re not in that big of a disadvantage if you use a controller.
A usual go-to for every PVP is keyboard and mouse+controller style movement so you can just adjust a bit to no Q lock and you will perform on the same level.