"This feature was rarely used and had problems with spam/abuse so we’re removing them to focus on other creator tools. You can still use your own captions, automatic captions, and third-party tools and services."
That seems fair enough to me. Creators can still add captions, it's just viewers that can't add them without a 3rd party service.
Some people are arguing about a reduction in spam or abuse, but it might also be a liability issue (but I don't know how or why).
My preferred solution would be better filtering and abuse handling, but at the moment this feature is a very mixed bag at best.
I suppose Google thinks auto-captions are enough to satisfy the ADA. We'll see.
What they should and hopefully will still do is - allow it to happen still, but give control to the content creator to authorise it and only authorised is public. That way you get the best of it all. Then you would have a way to acknowledge any abuse/spam and get on that instead of liberally tarnishing all community captioners as spammy evil people who should be stopped as that is how they are doing it. Playing the, we're doing this as bad things happen focus and utterly and completely ignoring every positive good aspect of this. A pattern many a company/government uses and still don't make it right. This approach is what I call "Think of the children 2.0", same thing in effect, just more meanutiatered and subtle approach and yet still heavy on the blinkers.