Why oh Why?

That's a pretty good question, and probably not as simple as the author tries to sell it.
Maybe both sexes have hunter's instinct to chase whoever is trying to escape and feel mildly uneasy being chased?
One thing is certain - from mom's and grandma's teachings to Cosmo magazine - girls are conditioned to please, serve and be nice, while boys are not.
Obviously in some cultures more than in other, but even in the wildest of western societies it still happens. Add general nervousness about eventual failure (yeah, if you don't get yourself a mate, you must be some kind of a loser), mixed sygnals and contradictory messages from family, friends, opposite sex and the media and it's a disaster ready to happen. Too mellow or too agressive, to slow or too fast, too serious or too easygoing - nothing seems to be right. Unless the man is totally in love anyway, there's a million and one way to screw up. Of course, men never screw up in relationships, just like they are never fat - they just enjoy their food and don't have enough time to excercise.
So the screw up happens and it's all the girl's fault - what does the gentleman do? Turns around and either chases some true bitch or orders a mail bride from Asia. Go figure.