I was waiting for someone to ask about this!
A bunch of people myself included have been hella cleaning up topics. Topics that aren’t directly relevant may be removed, also topics that aren’t actually a topic e.g. “I like birds” on a question about birds, will be removed as well. Also like @andrew said, a ton are still disabled. If they make sense to the question, they’ll be left alone :)
@bob_ RE: Applying a grandfather clause: That wouldn’t necessarily be a smart thing to do because the topic pages are kind of like directories of knowledge. If we left crap topics and unrelated topics on questions, those knowledge directories wouldn’t work as well and there would be a bunch of stuff that wouldn’t make sense. If someone wants to know about sandwiches and went to the sandwich topic page, they’d have to sift through a mess of unrelated stuff which would most likely be really frustrating. It would also defeat the whole purpose.