This ignores that community servers basically invented client anticheats. Almost all the current 3rd party anticheats started for community servers. Even Quake 3 Arena was updated with Punkbuster at some point.

You still see this with modern day servers. Modded GTA V, FiveM, had additional anticheat even before the unmodded game added anticheat. Part of the appeal of CS2 servers, Face-IT and ESEA, is the additional anticheats.