GitHub has 6 pages of public repositories (https://github.com/github) that you can peruse. To pre-empt your response, yes, they aren't all open source projects that GitHub has released. But a great many of them are. Some of their popular projects include things like Atom, Hubot, Boxen, Linguist, and many more.
They also have developers who contribute to a great many other projects as part of their daily work; Ruby springs to mind - Aman Gupta and Charlie Somerville have contributed quite a lot. And they pay at least two people to work effectively full time on git itself.
But don't let facts get in the way of your rant.