The side-by-sides that show how Go code is closer to the current TS code (visually) than C# would be are pretty compelling. He made it pretty clear they're "porting" not rewriting.
After reading the long Github thread, I think you're right. It's probably just as simple as "what is the easiest way to copy our TS code 1:1 to a faster language". And this case Go wins due to its simplicity.
What's funny is that while I understood a chunk about why that made that decision, a ton of things they were talking about went over my head. But then we they showed the side-by-side, I was like "Well that makes sense".
The side-by-sides that show how Go code is closer to the current TS code (visually) than C# would be are pretty compelling. He made it pretty clear they're "porting" not rewriting.