One of the problems for subreddits is people coming from the front page or from other subreddits, who are not part of the community of that subreddit, and begin to downvote things etc.

HN is lucky in this regard; there is just one HN, not uncountable “sub-HNs”.

Of course people can still come from other places to HN. But to earn downvote privileges here you first need some amount of karma. So hopefully this makes it so that downvote privileges on HN are mostly handed to people who are at least somewhat aligned with the broader community here.