As long as sub forums can be created easily, users may pick their sub forum and thus indirectly moderator.

In this setup having users elect the moderator leads to cases where small groups create their special interest group and then some trolls challenge the moderator.

Their may be some oversight on the large sub forum, but not all.

You see this in city-focused subreddits. But the reality is the name is power. New users type in their city and join the original one. The hostile mods suppress mention of the new one. It never manages to get critical mass.

Necessary for this is that subforums can't have unique names. If a bad mod can squat all the words like "computers", "programming", "coding", newcomers aren't going to know the best subforum is called "RealProgNoBadMod"