Community code contributions are no longer valuable. That's just the reality. Ideas are valuable, feedback is valuable, un-vetted code is no longer valuable.

Banning AI contributions is just the first step. Contributions are just generally no longer useful when given the idea you can have an llm do the work with 1/50th the effort it would take you before. Even with repeated rounds of feedback and correction it is less work to have an LLM do the work for you than it is to manage an eager contributor attempting the same work, and the result is going to be better and more in line with what you want.