It wasn't officially commissioned or officially adopted by Google to solve Google's coding problems as some believe.
It was merely initiated by a small team in Google, as their proposal for solving Google-scale coding problems. And has never been mandatory for new Google projects etc.
Go is ONE of the allowed languages, from what I know, but tons of stuff is written in Java, C++ and Python with no intentions of switching.
All those years, only a few, and basically trivial with respect to Google's needs, use examples for Go have come out of Google-land (a proxy/balancer for MySQL used in YouTube, Google Downloads caching, etc).