If all it provided was an API server then it wouldn't really matter. But this is pitched one level down ie: you can integrate this into your existing app as a library and expose it. I don't know what the utility of that is, but I'm kind of assuming it might mean you can add in interceptors and business logic to customise the API behavior which I think is pretty useful.
So the fact that it lets you do this with any JVM language is actually a key property that gives it very wide application.
So the fact that it lets you do this with any JVM language is actually a key property that gives it very wide application.