Thoughts on the "Grease" phenomenon

I've had a number of things simmering on the back burners of my mind, and one of them is the "Grease" phenomenon: stories in which a socially conforming character transforms into something (supposedly) excitingly transgressive to make a romance work out--as in the musical Grease. The girl changes completely; the boy, not at all. (The genders can be reversed, though, as in stories in which a manic pixie dream girl stories transforms someone who's supposedly, or actually, stodgy or straitlaced...