So what is your non-cesspool forum example that isn't Reddit? Twitter seemingly got taken over by bots early on, Facebook pages were a disaster at least when I was in college, and those are the big ones.
X optimizes for engagement and as studies have shown, that means optimizing for rage bait.
Reddit optimizes for rage bait too but includes a voting system that hides unpopular opinions, so any person that conflicts with the majority is marginalized. So on top of being full of rage bait, its an echo-chamber and that is before even talking about the powermod problem.
HN is much like reddit in style, so fundamentally HN also tends towards an echo chamber.
And by echo chamber, I mean a cringe circle jerk: a New Yorker article called it "performative erudition".
Gotta say though, it's rich hearing this from New Yorker.
Also using reddit as a baseline is like using a cesspool tank as a baseline of sanitation.