We are biased , as HN users, to prefer text-based, minimal, UIs that lead to (mostly) insightful conversations. Reddit on the other hand caters to a hivemind type mentality that loves things like emojis, karma, dramatic posts, etc. The current UI definitely favours that, and I think generally teens/young adults prefer that as well
HN is not free of hive mind effects, and I imagine most users here are also the type that seek “high engagement” material at least time to time. I’m guilty of it myself as recently as early this year. But reddit is intolerable to the point I don’t visit it aside from it being the default for search results.
I think teens and young adults merely tolerate it because it's what they've been given. Any seemingly positive embrace of such drivel is actually an adaptation of it into something more culturally meaningful and better coded to elude boomer advertisers' prying eyes.