Evolution selects for this. For the entirety of human evolution, it has been vastly more costly for women to reproduce than men (I don't even want to try to calculate how many children a man could produce in the 9 months it takes a woman to gestate one), so evolution rewards us for being as selective as we can get away with.

Maybe the grass is always greener, but having to lower your standards to some slightly less attractive women for your genes to propagate doesn't sound too bad compared to having to be the one to grow a human in my abdomen.