Another thing is user friendliness and maximizing engagement. Whatever Facebook did around 2015 or so to make everything bloated, animated reactions, and slower seemed to make things more user-friendly for a subset of less technical users, such that people who can't fact-check obviously fake articles and spam posts are enabled and incentivized to post as much as possible, and adding algorithms on top of that to maximize "engagement" make these things inevitable.
Twitter's chronological got turned off as the default at some point for a similar algorithmic "for you" page that I think has also made things worse for their platforms.
No idea about Quora, but eventually for ad-supported sites you start maximizing for time on the site and getting people to look at ads, rather than "quality" in the content on your social media site.