Generations ago, both males and females matured with the knowledge they would get married while they were young adults.
So each, would approach the "mating" ritual (dating) for that purpose of being paired up with your life mate.
So, men and women judged each other for that purpose and motivation.
Today, young women and men are encouraged to experience much before settling down.
For many women, this includes a certain amount of sexual experiences.
When a woman is looking for "experiences" she is looking for different qualities in a man, than if she would be looking for a life-mate...
What ends up happening, is 80% of the girls are chasing 20 or even 10% of the guys.
Once she sleeps with an alpha man, even if she is not an alpha herself, she feels that she can have such a man for a life-mate...and it is not the case. So she waits, and ages, and then the men she could have got are no longer there.