Reproducing.

Men reproduce by s3x0rring as much as possible, a man could have 1000s of children. However a woman cannot have 1000s of children, even if she doesn't have to look after them since she has to grow and usually raise each one. So men are attracted to sex more than women and has more of an urge to do it so there is loads of porn to satisfy this urge. Women must have evolved to be attracted to getting pregnant and raising children, so if women don't get as pregnant as they did in the past, why isn't there porn to satisfy their maternal needs?

They have a lack of needs.  You just answered your own question.  They want sex (and thus porn) but they don't want it as often as men.  However, you can also count "chick flicks" as porn for females because they're all about relationships and nuturing.