Go is geared towards productivity. If you have a problem you can solve adequately in Go, why not just do it in Go?

Because they gained popularity roughly around the same time many people think they are competing languages, but they're really not.

Ruby is my main programming language, if I need something to be fast and/or light weight I switch to Go, sacrificing some comfort. And if I need absolute lowest possible overhead, I switch to Rust, sacrificing a whole lot more comfort. Rust is more expressive than Go, but if your Go project is so large that it needs a stronger typesystem in my opinion you should switch to a language like C# or Scala.