Downvotes increase engagement. Otherwise they wouldn't have been put there in the first place.
No, the real issue here is too many of the "right" things are getting downvoted. So when The White House, Disney or the Academy disable downvotes on part or all of their videos but other wide swaths of videos don't need to disable downvotes, the contrast causes them to stick out like a sore thumb.
It calls attention (also known as engagement) - but not the kind of attention those who run social media companies want. Attention that is counter to the desired narratives is unacceptable. So here we go with the lame excuses that are all the sudden relevant when they weren't when the like/dislike stuff was instated decades ago?
Give me a break.