One person causes problems. They are dealt with, and come back. Eventually, they are "completely" dealt with.
So one of the bad ones was dealt with. That's no guarantee against more. And the deletions haven't dealt with all "inappropriate" content. Just some. They've also been sporadic, one thread locked, another deleted.
This kind of thing will always be an issue. It is a fact of life for groups like this on the internet. Sure, steps can be taken to minimize the impact of such individuals, but it is near impossible to "remove" them entirely.