What's the issue with giving out kernel mode access? Almost everyone is gaming on single user systems anyways.
Most of the other kernel anticheat rootkits are more polite and don't run until a game starts them, at least.
In general having a bunch of random stuff from video games running with kernel permissions is spooky. You never know whether someone will find an exploit in one of them, or if it will cause performance, stability or data integrity problems.
Honestly, if I was responsible for building an anti-cheat system this is the way I'd go about it. Anything that can run that you don't know about (e.g. because it ran before you started) is a potential risk.
Aren't there some security benefits from trying to confine apps to user land?