Because women take what's for granted, what comes to them, they dont chase after someone, its usually the opposite for men.
There is a sexual urge deficit between men and women, so higher demand from men, while the amount of women into sex remains the same, thus they have a lot of room to pick from.
Also, women are into romantism, and ever since they're young, through books, disney movies, series, even phone games, they grew up with that "prince charming" concept in their minds, they expect someone perfect to come in their lives because thats what they always dreamed of, so they subconsciously have very high standards, because they expect to have their own love story, with a hot, but genuine and kind guy, wich should also be somewhat mysterious and shit so the whole adventure becomes even more thrlling, you know what Im talking about.
So combine the fact that they're mostly inactive in a relationship, that they have a lot of room to chose from compared to men, and that they have very high expectations from their future lover, and you get what a woman is today, extremely picky by nature.
Its like if you were born a rich kid with shit tons of toys without having to do anything to get what you want, cause dad and mom love you so much they'll offer you anything on command, you'd be bored with your toys and would constantly take things for granted, thus, you find no joy in playing with those toys, the only things that you would want are the things that you dont already have, AND that are hard to obtain because too expensive even for mom and dad, then you'd constantly dream about that one super expensive toy, thinking about this toy, making research on it, looking for sales, is what keeps you active and out of boredom.
This is the same for men, you need to be superior, the "alpha male" concept is real, you need to stand out, with look, money, fame, skill, kindness, whatever makes you unique, but also, dont orbit around her, be that "expensive" toy.