YT says it was subject to abuse.  /r says

"No corporation wants their advertisements playing on a widely (and visibly) disliked video. Advertising is a game of positive associations - having your ad play in front of a video that the viewer is predisposed to view negatively because of the dislike ratio is never good.

So removing the UI element that would predispose a viewer to view the video negatively is a good step in reducing brand risk and increasing ad buys.

It also makes the experience objectively worse for viewers, but why would YouTube give a flying fuck about that? We don't make them money, advertisers do. "

There is a deep disturbance in the balance. : assholedesign
https://old.reddit.com/r/assholedesign/comments/qrtcw1/there_is_a_deep_disturbance_in_the_balance/

I'd prefer to see a feature whereby advertisers could suppress their ads on a video where the like/dislike ratio was not to their liking.

/r is not happy about this

https://old.reddit.com/r/funny/comments/qse6gd/maybe_it_was_because_of_what_happened_to/