two reasons....
1.women can get laid whenever they want to....with some exceptions for age and ugliness
2.women want it less*
*that's not at all to say women don't want it....they very much do, but men are just stupid about it. It's almost like evolution wired us to want to put our weeners in ladies or something.
Because men are socialized from a creepily young age to consider sex as something they are owed (along with so many other birthrights that society seems to think unfold from having a dick), while women are socialized from a creepily young age to not think much about sex (at best) or view it as something they owe to men (at worst).
That's just how patriarchy works.
I just wanted to say that this juxtaposition is hilarious.