AT
Cake had it. Why didn't you get it then? It didn't work very well and I'm sure it lost plenty of programming time for Cakewalk/Gibson ... hey, maybe that is part of the reason they went bust.
They was not investing into it. The final words was clear - Codewavers have tried to implement missing calls, the result was somehow working. The same you can get running Sonar/CbB in Wine under Linux, except the protection, it works.
But that is not native way to run things and Sonar/CbB is using relatively "modern" MS technologies. So cross-platform running is far from perfect and cross-compiling is not feasible. If you want to see how both ways can work in practice, in case "modern" MS technologies are not involved, check REAPER. It works fine under Wine and could be cross-compiled with Cockos own Windows API wrapper (btw open source), under OS X (official) and Linux (permanent beta).
@OP: I guess you have never tried to port a history heavy application which use threads, tight integration with hardware and OS specific libraries from one platform to another. Technically, they will have to completely rewrite the whole program.
But for what? "A Mac" is just single manufacturer PC with a custom OS. It is a wonder they have survived so far, mostly they can say "thanks" for rather bad drivers and using 1-2 questionably components in other PCs. But for how long that can continue? They was keeping iPhone as "you have it or you have something worse" for long, but that time is already over (after Samsung/LG/HTC, followed by Huawei, have managed to more or less optimize the software for the hardware). You can have full flavor PC in form of a tablet, which effectively evaporate iPad as "the only good one" in that segment.
If DELL (IBM/Lenovo) can manage to write a bit more stable drivers and can put $0.05 more expensive cooler on correct place inside notebooks... someone will ask "are you still using that outdated platform with an apple logo? why???"