It's just that writing a good web framework is actually way more complex than just a router.Martini,Revel or Gorilla are not webframeworks.
I believe Go is too rigid to allow something like Rails or Django. Go is for people who want C like performances with memory safety and easy concurrency. Go is not a "typesafe" python, at least it doesnt work like one until now. But I wouldnt be surprised someone comes up with a language built on top of Go that looks like a "typesafe" python or a Go++. That's what happens when people dont get their "nice things".