It’s been happening for half a century through six or seven generations of females, each of which seeks its own identity with a different lifestyle from previous ones.
Women possess some male hormones, and I use testosterone merely as example. Hormones respond to behavior. The more masculine-like is female behavior, the higher the level of Big T. The higher the level, the more masculine they act in response, so hormones and behavior trigger more of the other and spiral upward making women more like men. The reverse is true too. The more feminine women behave, the less T floods their body and the less they act like men.
Most men want to marry a virtuous woman, but she’s not virtuous enough unless she’s fascinating to him. Except for sexual potential, men see little or no fascination in women who act like men. Such women possess too few of the virtuous qualities that fascinate men.
Consequently, over 50 or so years women migrated from potential mates to undesirables for permanent relationships. They depend on romantic love to support their relationships. It fades in a year or two after conquest, and men are free to move on to another sex object, if they didn’t move on before.
The unisex movement is political and sprang out of Feminism. Ergo, feminist thinking, theory, and belief are responsible for short duration of marriages. But it’s really not that simple; that’s just the foundation. Unisex politics convinced women they should act more like men, which flooded them with more testosterone, which brought out more self-centered female aggressiveness that men find unpleasant, which cost women much of their non-sexual fascination, which lured men into sex-only relationships, which brought about the shortening of marriages.
The more feminine that women behave, the more likely they appear fascinating to men, and the more likely men see promise in them as lifelong mates. They are made that way in order to live compatibly with each other.