It's a fair question, although people kept phpBB boards running for years as hobbyist projects with decent communities on them and moderators are usually volunteers. We don't necessarily want tight-knit communities to scale to Reddit's size anyway and the only thing that's really changed other than Reddit eating the wind out of their sails for those types of self-hosted communities is that search engines are worthless spam-serving tools now so they're less discoverable which the fediverse seems like a decent enough solution to.