Tbf he just didn’t mention the reason he liked it, but to me it’s obvious. When you don’t have near real time notifications of replies or any at all, there’s much less of a chance for a flame war

Did something change on HN that users had to be conditioned to accept? No. It's a simply a different experience that is one among many that people continue to engage in. It's not like users "condition" themselves to only use HN.