Github's payment plans don't work out well for a team that's doing lots of small repositories.

My team is pretty small (5 devs) and we easily have 150+ repositories for different packages that all get wrapped into our main product. Github charges per private repository and 125 repositories maxes out github's organizational plans. Hence, we are currently on bitbucket.

The team also didn't want to have to make a business justification everytime someone wanted to fork a repository or throw something together experimental. We would rather just be free to create as many repositories as we please and not have to concern ourselves with the question of whether it should be a public or private repo.