We pretty much knew this is how all social media works, becuase a) engagement is what they want, why wouldn't they be optimizing for it, and b) how else might you measure 'quality'? Back when this started, I have no trouble believing some well-intentioned engineers thought that engagement was a good proxy for quality. A bunch of users give it the "like", isn't that a collective assessment of quality? Who is to say what quality is, overruling the users in aggregate?

I agree it has the negative effects you mention; and I've read lots of people writing about this, it's of course not a new observation.

But I agree it's good to have an explanation of what's going on, even when parts of are what we basically knew was happening on all social media networks. confirmed is better than "basically knew", for understanding how these things that effect our experiences (and our society) work.