If only Go was useful in building closed source products. Google must not have gotten the memo about Rust yet.
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).