One factor I haven't seen mentioned is the catastrophic decline in quality of Google search. That started pre-llm and now the site is almost unusable to search web. You can access something you know exists and you know where it exists, but to actually search..?

Most SO users are passive readers who land there using search, but these readers are also the feed of new active users. Cut off the influx, and the existing ones will be in decline (the moderation just accelerates it).