The shock is that someone at Meta looked into these studies and decided not to take actions to fix it because it might hurt their revenue.
[0]: https://www.nytimes.com/2021/10/10/opinion/instagram-faceboo...
I'm beginning to suspect that maybe we're told this too often, so we're starting to take it for granted that correlation can't be causation. But the saying actually only means that correlation is not necessarily causation. Quite often, correlation is actually there because of causation.