What network effects does GitHub have? Every repository is independent. It's like saying GoDaddy has network effects.

Everyone already has an account, so there's no friction to opening up issues, adding thumbs up to issues, using the discussion forum, etc. And while I think it's pretty silly, a lot of people take "10k stars on GitHub" to be a positive signal, and you can only get there when you have 10k people willing to star on your platform.