My only explanations for the lack of gaming support (see historical lack of proper OpenGL support) while still supporting high end graphics use cases (film editing, CAD, visual effects) are:

1) Either Apple wants to maintain the image of the Macbook as a "serious device", and not associate itself with the likes of "WoW players in their mom's basement".

2) Microsoft worked something out with Apple, where Apple would not step significantly on the gaming market (Windows, Xbox). I can't think of another reason why gaming on iOS would be just fine, but abysmal on MacOS. Developers release games on MacOS _despite_ the platform.