go-endpoints | Cloud Endpoints for Go | GCP library

Product manager Dan Ciruli answered this on the google-appengine-go mailing list :

There are two primary reasons, and the second is a byproduct of the first. We've had much less uptake on the Endpoints Go framework -- perhaps because, in the words of a developer I spoke to, "Go just isn't a 'framework' language." Unlike, Java, Python (and, say, Node), most developers using Go don't use a framework for writing an API backend.

And, at least partially because of that, we aren't staffed on the Endpoints team to build and support a framework in Go.

He added:

All hope is not lost. You can put a Go API behind Endpoints today on GAE Flex or Container Engine (without framework) using the Extensible Server Proxy. And later this year, we should be able to get the ESP deployed in GAE standard environment, you'll get the full power there, too.