Here's the FAQs, where they explain the decision to go with Go and not, say, rust.

https://github.com/microsoft/typescript-go/discussions/categ...

Hejlsberg also says in this video, about 3.3x performance is from going native and the other 2-3x is by using multithreading. https://www.youtube.com/watch?v=pNlq-EVld70&t=51s