That's a tough one, the dopamine hit is real and encourages engagement, which drives up the active userbase and makes for more opportunity for discussion.

They get abused too but a forum with none of it won't grow in nearly the same way as one that makes use of it. People like to earn something (karma, upvotes, whatever) even if it has no tangible value.

Honestly, reddit kinda nailed it but then made it very hard to keep supporting them when they took a steaming shit on the mods and massively overpriced the api to ensure they had more control of the userbase.

Overall I don't think they're hurting too badly from it though and I'm sure the extra ad revenue they get from ensuring everyone uses their app helps to dry their tears. Probably a smart business decision (at least in the short to medium term), depressing as that might be.