The OP thumbnail is brilliant, but missing at leaset one reaction layer. Of coures I've seen videos were the "youtuber" was reacting to someone's reaction to something, so...
... and this wouldn't be that bad, were it not for the fact that people gaming the algorithm with stupid low effort content works.
Not even just the reaction videos anymore. Basically 100% of my YouTube feed is shocked faces and I basically only follow educational YouTubers and some fairly mild hobby channels
I forget the legal term, but it's because they are commenting on something. So they're allowed to take someone else's content, add very little to it, and still host it on their channel.