Average user input quality is not optimal by definition. SO's upvote system and reputation system is what really refined quality. Much like Reddit's system is helping a lot for conversation. Much like academia's publish and citation system is an even better system.

I'm not saying LLM won't be able to train further, but tough and sound reviews are paramount to improving the corpus of quality content. And with the replacement of SO by LLMs, one can wonder if one quality system went down the drain. Anyway there's still code reviews on GitHub and in private repos, but we're still far from getting the human judgement out of the loop.

You can train on questions, but I will rarely answer to a chat with a SO-quality answer.