They have an imperfect rate-limiting and shadowbanning system which has a decent average-case. It relies heavily on consensus, just a couple downvotes in succession will prevent you from responding or clarifying your position (which can easily flip consensus), and a couple posts like that will have your account shadowbanned forever.

This trips up new accounts pretty much instantly. And so new views don't last, extreme views don't last, and people that don't know the community nuances and rules don't last. There is also no way to recover from the bad states of an account. Once flagged, always flagged, it doesn't have a cooldown method to revert you to normal status or build up into higher status. The shadowbanning keeps people busy as they don't know that people don't see their post for a long time. Slows them down in trying to circumvent the shadowbans. The mods do know when a user tries to circumvent a ban in a variety of ways, but don't say anything until they act up again.

The average case and best case of this algorithm is that quality persists, because the community nuances and rules are quite good. The worst case is that its an echo chamber, but that's not different than everywhere else. But at least those places acknowledge it. This place kind of sort of believes in the idea that non-consensus ideas can be presented "substantially" and they'll survive, in practice that's not very true.

In conjunction with all of that there is active moderation.

Also its against the rules to talk about the rules/karma/upvotes/downvotes. So we'll see.

I recall registering on HN years ago and posting the URL to some side project I was working on. Since it was a new account, I triggered some shadow-banning mechanism, and my project got no attention whatsoever. It was very dispiriting. Over the next few months I toyed with some new accounts, and I got lucky: one of the accounts didn't trigger the shadowban, and I quickly posted my side project (It was a 'Show HN').

It got like ten upvotes, and 2-3 comments. And that was it. It didn't get to the frontpage and lingered in /newest for a day. Getting stuff on the frontpage is purely hit & miss, and nearly impossible to game since the mechanisms in place for HN in detecting voting rings works really well, alongside the moderation aspect, and the way the community flags obviously spammy content or political flame-bait.

This is basically a subreddit. Just with better quality of community. That’s why.

You think it is because you agree with the average HN visitor and the mods.

There are people who sometimes complain that HN doesn't tolerate dissent or certain topics.

I will say that the anti-spam measures work unusually well though. I believe it's because of a lot of software tuning by the mods and aggressive community moderation.

Half the interesting stuff gets lost in “new”.

Community driven is the key I think.

Let's not forget the time where the 30% tax refund Apple misinformation spread like wildfire on the front page