Because the thing is, kind people aren't friends with assholes, and they're not really interested in making friends with the friends of assholes either. The social cross-pollination breaks down. So if you're stuck in the asshole bubble, I bet it can feel pretty lonely.

To be clear, the asshole bubble isn't actually trying to keep anyone out. The asshole bubble is quite inclusive. Anyone can surround themselves with assholes. It's the assholes who are in exile from kind society.