The reason the Go developers cited is fast compile times, as well as the belief that LLVM is "too big". I don't agree with these: LLVM compile times are fine for ahead-of-time compilation, and LLVM is big because it does important things.
I do have mixed feelings about LLVM for safe GC'd languages, though. LLVM is full of undefined behavior, and its support for precise moving tracing GC is not widely used. So I can definitely sympathize with not wanting to use LLVM for Go, but not for the reasons they cited.
