because most of their revenue comes from the sale of hardware. Once their superior software is ported to ix86, they will lose out on a lot of hardware sales (or so it is perceived).
I heard that there is some independent venture to port MacOSX to ix86 but i don't know much about it. I suppose Apple doesn't mind this since it expects the results to be substandard to their Mac/OSX tag team, besides, they will know that the independent porting situation will always be playing catchup to the real MacOS(X).
also, as long as MacOS is only able to run on Apple hardware (and only hardware from the last few years at that), the OS can be optimised for exactly that hardware. What with the thousands of endless differing hardware combinations available to a PC owner, the compatibility issues would be phenomenal for a start. I don't think people would be happy with buying a MacOS that claims to run on a PC, then getting it home only to find it only runs on hardware that is less than two years old... (which would be fine except for their yamaha sound card and their old external non-V90 modem that isn't supported and probably never will be, you get the idea...)
[ May 09, 2002: Message edited by: Calum ]