I bet you that these projects have AI contributions. The regular contributors just know their codebase a lot better and can instruct AI to make edits that are conforming to guidelines. The AI contributions they are banning are probably breaking code styles, conventions, are too broad, etc. and as a result creating more work than solving problems. I think the more honest approach for a lot of these projects would be to limit contributions to certain accounts - but then that would probably violate some of their egalitarian understanding of code development.