alt Hacker NewsGo was created because Rob Pike hates C++, notice Plan 9 and Inferno don't have C++ compilers, even though C++ was born on UNIX at Bell Labs.
As for compilation times, yes that is an issue, they could have switched to Java as other Google departments were doing, with some JNI if needed.
As sidenote, Kubernetes was started in Java and only switching to Go after some Go folks joined the team and advocated for the rewrite, see related FOSDEM talk.
A lot of people hate C++, that doesn't grant you the ability to make a language, however very few have the opportunity to create a new language out of free time provided by said language taking too long to compile.
I do not know why they did not go with java, I imagine building a java competitor (limbo) and then being forced to use it is kind of demeaning. but again, this would all be conjecture.