Expensive. That's basically it. We are using Bitbucket for that reason. We aren't a large team, but we do have quite a few repos. On Github we'd be paying $50-100 per month, on Bitbucket we pay nothing. Not a big deal for a heavily funded company, but we're bootstrapping for the most part, so it's a big deal for us.

Of course that might not be a sustainable state of affairs in a big picture sense, but it works for us for right now.