What price are you talking about? They're adding a map that offers a bit more leeway when working with it from several goroutines, is all I am seeing without thinking extensively about it.
I was doing that with Turbo Pascal 6.0 and Borland C++ 2.x for MS-DOS with Turbo Vision and TObject as interface{} in 1993.
If you are sharing a map in this way across many goroutines you are probably "doing it wrong" in go anyways.
You can still write your own specialized error-prone repetitive containers for each and every type by hand.
Yet, once a language has generics, people don't use the old way even though it's still possible to.
Perhaps that's because it has no place when there's a replacement which is less error-prone, less repetitive, more usable, and can be implemented once in a library and used forever.
Outside of that, agreed.
Two lines? I think you underestimate what's going on in sync.Map: https://github.com/golang/go/blob/master/src/sync/map.go