I think communities feel alive when members feel like their presence matters. People post, get responses, recognize familiar names, and see ongoing conversations they can jump into. There’s a sense that something is happening even when traffic isn’t huge.
Empty communities often have content but no interaction. Posts sit unanswered, discussions don’t evolve, and members feel like they’re talking into a void. Activity creates more activity, while silence tends to reinforce itself. The difference is usually engagement and connection, not just member count.