^^Because they are MODELS and very good ones, Christy has done truly alot of W covers and many of them are my all time favourite, and i preffer looking at a fashion image presented through model instead of celeb, they actually know how to pose and make the photograph memorable, not to mention many of them look better in the clothes than celebs.
But of course i understand that magazines are in the buisness of selling issues and making money, its just always nice to see a model cover to me.