The problem is that submitters often do not feel responsible for it anymore. They will just feed review comments back to the LLM and let the LLM answer and make fixes.
This is disrespectful of the maintainers' time. If the submitter is just vibe/slop coding without any effort on their part, it's less work to do it myself directly using an LLM than having to instruct someone else's LLM through GitHub PR comments.
In this case it's better to just submit an issue and let me just implement it myself (with or without an LLM).
If the PR has a _co-authored by <LLM>_ signal, then I don't have to spend time giving detailed feedback under the assumption that I am helping another human.