But Youtube isn't a monopoly. It's competing with Netflix, Prime Video, Hulu Instagram, Tiktok and Twitch off the top of my head. So they do have to make Youtube competitive

Your theory of

> just a way for some product manager to fluff up their metrics for a promotion.

is the most likely culprit

It is a monopolist in the format it specialises in - medium length 'creator content' that the creators typically post every 2-10 days. Some do post to Nebula and Patreon, but really, there's nowhere else to go for that kind of content, and that's the content that most of their ad revenue is attached to.