Anti-cheat systems already have to make changes, since Microsoft have plans to significantly restrict kernel mode access after the major Crowdstrike issues earlier in the year. Kernel mode code is very invasive, difficult to get correct, and can result in major security holes or stability issues if not written correctly.
A bug in userland code may crash that one app. A bug in kernel mode code can (and often does) cause bluescreens, that people blame Microsoft for. I'm sure they're tired of being blamed for buggy code written by other companies.
Running the anti cheat code in userland will (in theory) make it easier to run on other OSes too.