As a community grows in size it becomes more diverse. As it becomes more diverse it becomes a better representative of society in general. As a result websites

As a community grows in size it becomes more diverse. As it becomes more diverse it becomes a better representative of society in general. As a result websites that target a niche audience tend to shift to websites that target popular culture as they grow. HN is technology and startup oriented and is populated by many professionals in those fields. A popular HN will be populated by people who want broader topics and who are not experts in any of them. And less disciplined individuals tend to abuse the moderation system until it becomes nothing more than the voting system of a popularity contest. Reddit, for example, was a great place for discussing interesting topics a few years ago. Today it is a website for memes. And the technology topics are moderated not according to how interesting the submissions might be but according to how cool and popular they are. The eternal September is not a new phenomenon. And this isn't limited to websites. It happens to TV stations too. SciFi has wrestling, History has ancient aliens, and MTV stopped playing music videos a long time ago.