We have been public about not using Go as the bootstrap language. We started with a compiler in C for a number of reasons, mostly for ease of bootstrapping but also to avoid making a compiler-optimized language instead of a general purpose one. Once the language was designed, we ported the code to Go for ease of maintenance and development.
Well here is a variant of that pattern: the TypeScript compiler is also being ported to Go: https://www.youtube.com/watch?v=pNlq-EVld70
The video is worth watching for the reasons why. Turns out a general purpose language is indeed a good compiler language.

YouTube
A 10x faster TypeScriptTo add to the answer for why Go: A post by one of the devs on github makes it clear that the biggest factor that favored Go was its ability to replicate the structure of the existing TS codebase with minimal translation.