They're trendy, that's it really.
Even though my brother-in-law knows nothing about computers and couldn't tell you the difference between a Mac and a PC, he get a Macbook for his birthday. When I asked him why he wanted a Macbook, he said I don't know, people said they're cool.
That's probably you're answer for 90% of the people that buy Macs, Macbooks, iPhone's, or whatever else. It's not because they know they're better or there's some particular feature they want, it's just that they're cool.
Ten years ago Macs were very much better at some things than PCs, today, not-so-much. They're just incredibly overpriced and really have no advantage over the PC anymore.
But hey, at least you'll look awesome sitting in the local bookstore cafe typing your screenplay.
