I mean you have to have a better reason to ban AI from open source projects than just bad code.

Limits on submission size and frequency could be placed on Human and AI equally.

Badly written code hurts open source, but humans are just as guilty of that as machines.

This hurts the open source community imho.

Nah. At worst the open source community is indifferent. If someone can pick up where this left off then it benefits the community.