OSX isn't even targeted for normal PCs and afaik not easily installable. And it has means in place to close the system, see https://developer.apple.com/resources/developer-id/ and the consequences. And yes, obviously talking about desktop-systems here, so Android is not fitting (and in this context subset of Linux anyway).

And I still think the different technical situation influences the situation, it is not only about the UI (and the jump not as big as the jump away from DOS).