I think a key reason is HN has (IMO) a well-designed vote-based moderation system. Flamebait tends to get downvoted/flagged pretty quickly, burying it where it belongs.
Contrast that to pure engagement-focused social networks like Facebook or Twitter, which do the opposite: prioritize showing flamebait, because people are engaging with it and therefore it must necessarily be quality content!
Contrast that to pure engagement-focused social networks like Facebook or Twitter, which do the opposite: prioritize showing flamebait, because people are engaging with it and therefore it must necessarily be quality content!