Edit: Ah, here's the relevant blog post: https://opensource.googleblog.com/2017/03/a-new-home-for-goo...
[1]: https://opensource.google.com/projects/ganeti [2]: http://git.ganeti.org/?p=ganeti.git;a=summary
For example, apparently AGPL licensed projects can't be used at Google: https://opensource.google.com/docs/using/agpl-policy/
Google no doubt has some proprietary code that they would like to keep proprietary. Also they probably have code under other licenses that they would like to remain under those particular licenses.
("page=6" means no 6x clicking "Show more", then it loads the whole page - interesting)
[1] https://opensource.google.com/projects/search?q=%20&language=r
[2] https://opensource.google.com/projects/search?q=%20&language=scalaOh, wait, no, they killed that one. In about a year....