I'm not sure it's anything mechanical. Facebook is a wretched hive of scum and villainy for sociocultural inertial reasons. You may as well ask why Detroit is a

I'm not sure it's anything mechanical. Facebook is a wretched hive of scum and villainy for sociocultural inertial reasons. You may as well ask why Detroit is a crappier place to live than Madison. Facebook succumbed early on to echo chambers, disinformation campaigns, and marketing of snake oil and pyramid schemes. Hacker News set rules and followed them consistently, moderating the discussion in accordance with those rules. Maybe for a better example, just look at Reddit. Something like AskHistorians or SilphRoad for Pokemon Go are terrific communities full of great information and productive discussion, whereas many other subs are as bad or worse than Facebook. That is in spite of exactly the same interface technology. The difference is culture. If Facebook has a design problem, it's not having any sort of guiding principles other than engagement. The purely algorithmic curation isn't really curation. It doesn't create a culture at all. It just creates addiction. Infinite scroll is in service of that, but it doesn't create it. In fact, the mobile reader I use for Hacker News has infinite scroll and it doesn't make the site worse.