The policy you linked explains its reasoning pretty clearly. So you feel better about their decision, please re-read it with an open mind and a "why would a very ideologically-motivated copyleft free software project think this" attitude.
Or get forked to irrelevance.
I don't think they'll be forked to irrelevance. Even if I put aside my skepticism of the quality or longevity of AI-assisted projects, I don't think there's a bigger audience for a Nura that's less principled on the issues they mentioned.
Linux uses LLMs. It cannot afford not to, when LLM can find and fix bugs at a rate no amount of human effort can match. This includes security-relevant issues.