Yeah that makes sense, if they collaborate and share information. But more-so it avoids the case where a patch drops then people suddenly get banned - it's easier to match the exact version and what changed or is different compared to others on the market that avoided it, which I think they want to avoid most.

I think ultimately it's to avoid devoting too many resources to the arms race by breaking it up into sprints. Mass ban waves also make community impact and news, and in some cases for the regular players it refreshes the scene just for a bit by clearing the muck. They can time it to coincide with in-game events or updates too then (which often break cheats), giving a window for non-cheaters to enjoy.