Verified answer

When you are a millionaire you tend to brag about how much you over pay for things so Apple being extremely over priced is perfect to keep up their ego and image

because only rich people can afford them.

ease of learning coupled with reliability.  All programs/apps that exist for Macs have been built and rigorously tested to Apple's quite high standards -- or they simply aren't sold via the Apple store AND can not be advertised as working on the Mac OS.