Is there any reason why Google isn't trying to use Google Code to compete with GitHub? Seems like it wouldn't require many more resources, and could give GH a run for its money with some niceties (free private repos, plugin to their cloud platform, etc)
It's also important to note that their support for SVN, HG, and Git is all an in-house implementation to work on top of BigTable.
I'm not really sure why they let it stagnate in the first place, but someone made the call that it wasn't worth investing in anymore. Remember that Google Code really came as an answer to SourceForge which was going downhill. But then we had GitHub and BitBucket appear, which have really taken over.
For pure source repos, Google has been using Gitiles[0] for most of their public projects like Android and Chromium[1].
Actually maintaining is costly. 1. The system around it is evolving, even no features are added, necessary upgrade is necessary to talk to the backend, and sometime it is nontrivial. And since svn is now not popular, should they add git support to the dated infrastructure? 2. Routine SRE works should be done, deployment to new clusters, oncall alerts. 3. Bug fixes. 4. How can the maintainers be rewarded? They are working on a project in maintain-only state, who wants to do that?
Basically, for hopeless projects, better to turn them down than make them alive in half-life.
It may have also existed at Google Code, I don't know. But this was the repo I was directed to after Google I/O last year.