There is so many ways of running your own code in the kernel (mainly thanks to signed, but terribly written drivers [1]) that PatchGuard really is only a nuisance if you need to overwrite some kernel functionality, e.g. for hooking functions.

So a rootkit needs to worry about PatchGuard, but if you only want to run code at kernel level, you generally don't.

[1]: https://www.unknowncheats.me/forum/anti-cheat-bypass/334557-...