Because the girls of the real world can never measure up.
For your consideration, the merits:
Snow White - into gang bangs and octo-somes. No non-porn star hot woman lives with 7 midget men. That whole movie could have been the first reality TV show. She also seems to fetishize slave labor.
Ariel - Probably gives GREAT head as that's all she has to offer. And it's probably even better under water! Con: ginger. Also her whole body probably has an STD called "seaweed" or something strange.
Jasmine - Cha Ching. Thats all I gotta say. Girl is made of money and has that middle eastern/persian exoticness to her. The baggy pants need to go, however I see potential that her carpet is truly magical.
Sleeping Beauty - Like a college sorority girl, it's apparent she is easy. If her story didn't scream "i make terrible decisions / get blackout drunk / get roofied in my morning coffee" then I don't know of a better example for you.
Belle - Hot and doesn't care what you look like physically. Probably safe to assume she has a vajayjay that you could send a spelunker down since she is obviously into beastiality. I don't think she'd be satisfied by anything a normal man could offer. But if you bring a Mastiff into the picture there's potential.
Tiana - Black. (never saw this movie)
Cinderella - everything about this girl screams "high maintenance." She thinks she's above scrubbing floors? LOL? Her annoying, elitist attitude (and the fact she'll be a terrible at homemaking) is only eclipsed by the fact that she is obviously for sale to the highest bidder. She's a hot monica lewinski. If you have the money you can probably keep her, but she is a golddigger.
Pocahontas - Her name actually means "loves to be poked by wang." You can't date her and have a conscience. She actually founded Greenpeace in the year 1499 and was the first native american to copyright the "single tear." She pines for the outdoors. Like camping? Like pine cone oriface plugs? Like getting nagged 23/7 for how you should care more for nature? You'd love her. But if you sneeze on her you'll probably kill her, as her immune system is whacked from too much peace pipe.
Mulan - The world's first feminist. She will samurai your member off and throw it in the rice paddies never to be seen again if you cross her. Still, theres something hot about her dominant personality and the fact she can kill anyone that you ask her to. If you're of asian persuasian, give her a look.