Why are bigger females attracted to smaller men?

I don't think that bigger females are attracted to smaller men, but they are so tall or big-boned and the average man is 5' 10" - 5' 11" that it appears that way. It's no different than saying "Why is that guy so attracted to tiny girls when he's well over 6 feet tall." You simply fall in love and size really has nothing to do with it. My niece is 21 years old and 6 feet tall; very large boned, but great figure and statuesque, yet she is still young enough not to appreciate how gorgeous she is and if I say anything I simply get "Awww you're my aunt and you'll always say that about me." It bothers me to see her slouch around when she is out or, her mother has told me that she often will just sit in a club with friends and refuse to get up and walk around if the place is well lit because she feels like a mammoth woman. Some men are the ones that like very large well-rounded women and choose the woman in their lives, not the other way around.