Fanfic never slowed down. It's just as prolific as it ever was.

I don't have a good reason for why you would find a lack of interest in the discussion or critique of fanfic. Maybe people proofread within their own small communities on Discord these days or with AI. Maybe people have become more resistant to the idea of their work being lampooned. Maybe there are no truly 'horrid' badfics any more or at least the idea of widely lambasting them on social media has gone stale because sensitivity and the risk of being cancelled outweighs the fun of lampooning peoples' work.

Maybe it's the fact that, at least on The Social Media Site That Will Not Be Named But Used to Have a Little Blue Bird, things have mostly turned into a culture of vociferous hate and, again, cancelling rather than good-natured discussion, lampooning, or less good-natured mockery of fics you don't like.