Each of these things need to be studied separately, IMO. As different social media sites have/less of each of these:
* Algorithmic feed - encouraging rabbit holes, reinforcing clicbait and ragebait
* Comment sections - encouraging pile-ons, and vitriolic debate
* Short form content - TikTok videos, etc, quick, snackable content and destroying people's attention span . Then there's the overall ad-based incentive to put all these together to keep you engaged. TBH the fact hacker news has a different model, makes me feel better about it, rather than caring if its social media or not.