That’s a good question. I don’t know.

Just speculating, the upvote/downvote does help a user know what is expected behavior and some understanding to build from.

It also provides a rich incentive to post because “number go up” feels good.

I’d love to know YouTube’s data on hiding the dislike button. It wasn’t great for viewers, but it may have had an effect on creator satisfaction. But I don’t know for sure.