HN started niche and attracted a narrow audience intent on productive communication; mostly college grads and/or positive attitude people (successful attributes, even if a bit rowdy and troublemaking at times), and not many lottery ticket buyers [1]. It is very open, so it could be overwhelmed by less signal crowds over time should it hit mainstream visibility.
Do some platforms need to limit the number of participants and do stack-ranking dismissals? IIRC, the ASW platform culled a bunch of accounts.
There have been studies on social media interactions (I can't recall the links atm, and am almost done posting from the loo :) and "captological" aspects that influence people's online perception, behaviors, and reactions. I think the problems are the people, the power they're given, the presence/lack of fairness they perceive, what they're presented with, and whether or not the community defends itself and its values strongly (I think dang does a Herculean job with this).
[1] Best characterizes the lottery ticket phenomenon: https://news.ycombinator.com/item?id=23393875