Acceptance is likely due to Ian Taylor being a long term GCC developer who is easy to work with, which mean that 1) the front end obeys the often unwritten conventions for good behavior, and 2) they know Ian Taylor will be around to (and capable of) fixing the various unavoidable problems that will show up. Thus, the new front end should only put a minimal burden on the other maintainers.

The merit of Go itself has likely been less of a concern.