My theory is just that if anyone can join, and everything is anonymous and there is no barrier to entry [1], quality of communication will just be low. Makes me think about how some Ham Radio enthusiasts want to keep Morse Code as a requirement to get a license even though it's not really needed, it simply acts as a good filter for keeping less prudent people out of the eco-system. For web boards, maybe September will never end [2].
Hope this all isn't too cynical and please speak up if it sounds so.
[1] I realize HN is easy to join but is often seen as having far superior discussion than Reddit. I think there's just something about heavily technical article titles and topics that make it a bigger lift to want to jump in with trivial but aggressive arguing. [2] https://en.wikipedia.org/wiki/Eternal_September