I've never worked at Google, but I've used Gerrit not infrequently at jobs and on projects--it isn't "random" even if you've never run into it before. Gitiles is just a hat on top of it; it's not pretty but it is fast.

It's not "developer hostile" to not use Github. Git works everywhere. It might mean that to contribute to an operating system a developer may have to learn how to use something that isn't Github, but honestly if that's a bar to contribution for somebody they probably weren't gonna anyway.