It's not that difficult since it was just one game. Apple never took gaming seriously, other than to use a game, one time, as vaporware to push product.Bungie was going to launch Halo for Mac and PC simultaneously, but then MS bought the studio in order to have a big first party title on its new console, the Xbox. That meant that Bungie had to completely overhaul the game to work on Xbox’s limited hardware, and they even dropped multiplayer because Live service wasn’t ready yet. When the game finally made it to Mac and Windows, it was a third party port. Hard to blame Apple for that one.
With the kind of money Apple has now it could open its own AAA studio. But, it hasn't and it's very likely it won't.
Just keeping OpenGL up to date on OS X wouldn't have been much to ask but it couldn't even be bothered to do that. Where is Vulkan? Apple could have put its might behind that standard to help to break DirectX dominance. But, no.