Some metric they're aiming to improve probably shows this change keeps users on the site a little longer.

LOL. I can see it now:

User: Nice video! I'd like to learn more, so I'll just look at the descritiopn. Wait, where's the description? Where did that stupid thing go? It's got to be here somewhere - Oh! You've got to click on it! Like fucking Christ why?? Why hide it from me?

UI Expert: People are definitely spending more time per video. Mission accomplished!

You know the PM is the one who ultimately greenlit the changes cause they can take credit for it.

or just "Engagement is up! people interact with the page so much more now!"

Google is Goodhart’s Law in action at corporate scale.

Every big company is Goodhart's Law in action, Google just hired the best metric maximizers so they are the best at showing it.

There's a pattern: they move a feature, making it inconvenient, and then remove the feature because it is not being used. See Google cache links for an example.

It's had a pretty short limit before it shoved things below the "more" fold for a while now if memory serves.