What hayasaka said is correct. From an evolutionary point of view, men are polygamous, while women are hypergamous. It is advantageous for men to procreate with as many desireable women as possible. It's just basic biology. Women on the other hand need to choose carefully, as she will have to sacrifie resources and time to create an offspring. Not only that, while in pregnancy, women will be very vurnerable and weak. Hence she will choose those of higher standing and wealth to ensure her safety and stability.