[dotancohen]

  > You can still dislike videos to further personalize and tune your recommendations.

2016 Dislike button: Feature to inform other users that a video is not worth watching.

2021 Dislike button: Feature to inform google to show _you_ other content.

Google is hijacking user interface concepts to slowly train users to train the machine about how to train them.

[password4321]

I think this is the key point: the signal is valuable enough for Google to keep it to themselves. Similar to the work done to hide referrer when clicking through searches (of course there's a good reason!).