Hmmm, it was almost certainly created because of past human nature. What you have to remember is genetically humans and millions of years out of date in regard to what enviroment our bodies are designed to live in. We are essensially still cave men and women, the only thing that really seperates us from animals is the (of bugger i cant remember what its called

) part of your brain that creates emotion.
Now, why would women become attached while men want to move on? This is basically what the MM method covers very early on, S & R value.
women are needed to replicate, yet they need saftey for both themselves and the children. However, men as a defult have more saftey value (i am talking cave man terms here, men were bigger/stronger) and therefore are looking to replicate. Now, whats the fastest way for a man to replicate? many women. 9 months is a bloody long time for a cave man (when u consider little medical knowlage and an average life span of say 30?).
However, this model no longer works in the modern day world, women are perfectly capable of saftey on their own. That is partly the reason i think PU is so popular, its so much harder now than say a few thousand years ago. Men still need to replicate, have the same urges etc etc. Women however are no longer driven by a need for saftey, they alread have it. Will it change? eventually. But would it be in the interest of human survival for it to change in the way you want tho? that would be the true question and if it would work.
/madals