Fascinating, I'd guess this to be the result of a filter bubble? i.e. it would only show you things you agree with. That might not be optimal though (at least in terms of harvesting human attention at all costs), I always heard that outrage drives engagement better?

I wonder if this is because the creators routinely prune negative comments of them. Or perhaps it is because Youtube severely down ranks comments with dislikes.

Because YouTube promotes positive comments and every comment section is set to "best comments" now by default (instead of most recent comments)

Toxic positivity is what the cool kids call it. Overtly positive, happy and encouraging comments that feel so manufactured and fake.