Dart is also Google sponsored and no one uses it despite the fact that it's actually a pretty great general purpose language. People use go because it's productive and had a PHENOMENAL standard library for networking.
It clarifies the fact that Go is successful for more reasons than just being pushed by Google. So it focuses the question to "what is it that people like about it". And then we can have a better conversation.
Your theory fails to account for the lack of success with respect to Dart; so, it seems more like something you have an urge to believe (despite a lack of evidence).
Dart has been abandoned by Google the day that Angular team has chosen Typescript instead of believing in Dart, thus sending to the world the message that the company doesn't believe in it.
Whereas there are a few production examples of Go at Google.
My understanding is that Dart is used by Google Fiber for their routers, so I wouldn't call that abandoned yet. But, the point is that Google supporting a language does not seem to imply its eventual success.
