The golang implementation of protobuf sucked historically (still does, but is improving) and gogo was an alternative that fixed a lot of problems and was nicer overall. Until its creator burned out and deprecated it. Chasing a constantly moving target that you have no control over is very taxing in the long run.
I think it's less that protobuf is a moving target, and more that gogo tried to add in all the features that google didn't want to maintain, and learned that maintaining a massive feature matrix was impossible.