As an example, C++ and Java programs at Google were taking more than half an hour to compile. This is why Go's semantics were chosen with speed-of-compilation in mind:
* Strictly acyclic module hierarchies (greatly simplifies compile-time name resolution)
* No generics (specialization has a compile-time cost)
* Unused imports are a fatal compilation error (to avoid having to parse unnecessary files)
All three of these decisions are somewhat contentious; Pike admits as much in many of his talks. But they were chosen because of the challenges of writing software at Google's scale. It is in this roundabout way that Go "belongs" to Google, in the sense that it addresses problems that Google has and prioritizes the best solutions to those problems, whether or not those solutions are at odds with the needs of non-Google users.
More a "solve Google's specific problems" language, general Google purpose