>But it does allow engineers, trained on one platform, to work on the other.

The programming language is the most surface level detail when learning a platform.

The libraries, the frameworks, the OS services, the app lifecycle, the UI idioms are the hard part, and those cannot be abstracted away (of course you can try, but you'll end up with an inconsistent mess that doesn't feel native in any of the supported platforms, at which point you should just create a website).