At that point why not use something F# or Rust? Both can provide comparable or better runtimes, very decent ecosystems, and they are already much better languages.

Because Go as an ecosystem has some really attractive properties that few other languages offer in the same combination: portability, stability and a strong compatibility guarantee, quick onboarding for new learners, a robust and scaleable runtime with GC that rarely gets in your way, minuscule startup footprint, reasonable direct control of memory layout when you really need it, a fairly large developer base and corporate backing/funding that's not going away any time soon

So I have to repeat the question: why not F# or Rust then?

None of that is too uncommon, with the notable exception that Go is better at the "quick onboarding" part since it goes out of the way offering no new concepts or syntax that have to be learnt; something that the comment I was replying to would like to change by introducing Optionals and Functors.