Well we don't :/ I've survived weeks on less than 4 hours sleep a night. We look prettier with more sleep though . That's a fact. Men don't have to worry about being pretty , that's a fact too. So I guess woman need more sleep so we can look pretty and men don't have to look pretty . I just sussed your question :E BAM !
You may need to watch this British Documentary to understand why female brains are easily overtaxed and need more recovery time than real brains.
(It's a joke, honest, please don't hate me!)