Another example: r/AskHistorians is so heavily moderated almost every comment gets deleted.

Their standards of quality are very high. It's not a sub to push your views or argue, it's a sub for historians or people who can back an answer with academic references. So most comments and answers will get modded.

It's oddly refreshing. No flamewars, no junk comments, no "everybody knows the reason X did Y is Z" because that won't be accepted by the mods.

It's not perfect, but it's good enough.

AskHistorians is far and away the best moderated sub on the site, but it relies entirely on guidelines that you can understand and agree with. Moderation on other subs (no clue about this one) is so heinously biased it makes them unusable. Very common on political and news oriented subs....