Well they are actually doing it, but the UNIX crowd is so inflated that most mobile OSes use a UNIX kernel that they don't see it coming.

Hint, for Swift, Objective-C, Java, JavaScript, Android, Dart, .NET, the kernel doesn't matter at all from the API surface point of view.

And I am only listing the official mobile OS SDK languages being forced on 3rd-party devs as you say.