I though they can detect that, why would they ask the users whan you can automate it?

I'd figure they need training data for their AI-detecting AI.

Or - I've heard anecdotes of audience disengagement, which the departed or cut-back users explain in terms of content quality falling off an AI-generated cliff. If that's a real trend, YouTube management might be feeling some existential dread.

automating this would be too complicated; getting feedback from a large number of users would provide more certainty

Good because damn, there is some AI slop out there.