When you visit
- Change repository names or descriptions;
- Delete repositories;
- Add an SSH key to your account;
- Fork repositories;
- Create pull requests;
- Enable and disable project features;
- Use the wiki and issue trackers;
- View graphs of statistics;
- And others.
That is—GitHub forces you to run proprietary software in order to use much of their website. This is a bit startling for a host that owes its very existence to the success and development of free software.