There's a demographic of gamers who only play the one competitive multiplayer game (such as Fornite or CoD). They don't buy many games, they're not the most lucrative market for game publishers, but they do keep those titles in business. And yes, for them, anti-cheat is important and they're unlikely to move to Linux.
Being in kernel mode does give the rogue software more power, but the threat model is all wrong. If you're against kernel anti-cheat you should be against all anti-cheat. At the end of the day you have to chose to trust the software author no matter where the code runs.
If malware does get executed in user mode it could take advantage of the anti-cheat kernel module to make the attack even more damaging to the OS.