I'd guess Go has one to avoid ending up with several like Java, to do Go-specific things like extract the dependency graph from the source code, and to have one

I'd guess Go has one to avoid ending up with several like Java, to do Go-specific things like extract the dependency graph from the source code, and to have one fewer dependency on the platform--I don't know much about how you build on plan9 or Solaris, I know go build is the same program on each. That said, go tools are canonical but not mandatory. If switching to this doesn't work for the protobuf foks, it's simple enough not to switch.