> Was it just the entry barrier and limited demographics?

Also possibly the difference in sheer volume of content and people. It's much easier to moderate when you have at most a few dozen people discussing a given topic. HN is dealing with thousands of people who sometimes, during really heated discussions like the GameStop ones, post literally at the same time and make more content than a single moderator or even a team of moderators is capable of reviewing, even with community help in form of reports or flags.