Reddit mods are volunteers as well.

Reddit's system ends up giving them enough dopamine (somehow, probably related to how users get it) to do it for a while. Forums aren't as addictive.

Seeing as people have been self-moderating some of these forums for more than 20 years, it's a solved, non-issue. Just because you're not familiar with this, doesn't mean it doesn't work. It's worked since the 70s with bulletin board systems.

Yes, those required moderation too.

Again, solved problem for community sites.