alt Hacker NewsStill has an anti-cheat, they just bothered to allow Linux support.
Companies don't do this out of laziness/incompetence, but even some large anti-cheats work on Linux and some games simply choose to not enable it (cough, Tarkov, cough). Their problem, I'm no longer gonna play games that don't work on Linux.
Funnily enough the best FPS game ever (Counter-Strike) runs absolutely fine on Linux. Thanks Valve!
As far as I know, all the anti-cheat options for Linux are not kernel-level, which means that they are drastically less effective at their intended purpose. That's why so many competitive multiplayer games choose to not enable it.