Yikes. Why anyone would willingly develop for Apple platforms is beyond me. But then I also don't understand why some some people like using the crap^WmacOS. To each their own I guess. Hardware does look nice though, too bad about their software.
Because they "have" to have the nice display or good battery life I guess. Everyone has different priorities. Personally for me it's Linux or nothing.
Well, gotta sell wherever the customers are, unfortunately.
Because that is where the users with the money are.
Well, mainly because it's a better unix than Linux for the desktop, and I'd rather pull my eyes out of their sockets with a rusty screwdriver than use Windows.
Other than developing my own (without using any other OS...) which is a ... significant ... task, there's not much other option. YMMV.