Why does it have to be that way?

Why is it that a guy would rather have a skinny woman with an ugly face...then a heavy woman who is beautiful on the inside and out? I don't understand this at all! All the guys hit on my friend who has a beard and unibrow...and her I am with gorgeous eyes and luscious lips...and flawless skin, but because I am a big girl, guys want to flirt with my friend. Please help me understand this!