I think that's a reductionist view. Platforms like Twitter are pretty unique in that unlike most other social media, you don't have well-defined communities org

I think that's a reductionist view. Platforms like Twitter are pretty unique in that unlike most other social media, you don't have well-defined communities organized around topics or locations. On Reddit or Nextdoor, you join to discuss specific interests, and that serves as "social glue" that lets you make new acquittances along the way. The same goes for HN, by the way. But on Twitter / Bluesky / Threads / Mastodon, you probably don't have anything in common with another user picked at random. The most common (non-commercial) motivation for joining is probably to just hang out with the people you already know from elsewhere, and then expand your social network very gradually and conservatively, mostly based on who they know. So it doesn't matter that there's 10M strangers over there if none of your buddies use it.