No, it was absolutely about the effort needed to rewrite the project. They couldn't afford a rewrite, only a port. They're not going to keep maintaining the Typescript version once they have transitioned to the Go version.

Yes, they distinguish between a rewrite and a port (first time I heard the distinction like that, but it intuitively makes sense).

A Go port looks roughly the same as TypeScript, same “shape”, same concepts, so they don’t need to re-architect the code, they can just “translate” TypeScript to Go, then clean up where makes sense or needed. For a good while (definitely years, probably half a decade, if you ask me) while both projects are maintained, adding fixes and features will be therefore easy. The two codebases can be expected to have almost the same output and bugs, both is good for maintainability.

With Rust, the translation wouldn’t work as Rust is significantly different. This would mean rethinking everything, the architecture would diverge, resulting in two possibly very different set of bugs. With different structure, tweaking both at the same would be very difficult.