If the comments under posts become too active, it is downrated and disappears from the front page which reduces the rates of people commenting on it.
https://news.ycombinator.com/item?id=16020089
You'll also note things like "when the comment is too deep the reply link disappears" which creates a bit more friction for carrying on what would likely be unproductive threads.
Things around controversial topics also get downranked (whereas on Reddit hot topics move to the top of the list).
There's a lot of automated tooling in HN that reduces the amount of manual moderation that is needed by making it harder to have posts that contain things that need moderation.
