Ive read about this a while back. One woman's opinion about it was the whole programming of women as they are growing up. They are programmed to be non-promiscuous, to strive for husband, kids and house. But she went on to say that at some point when the woman achieves all that, the house the kids and the husband, she gets bored because she has now achieved all there is to achieve she has completed her programming and is now bored with it. Its simplistic the way Im explaining it, she went into more detail, but thats the gist of it.
Not sure how relevant this is with the new movement of women in the workplace and having careers, but it made sense.