Promiscuous girls are called sluts... but why do guys get off the hook?

well we live in a male centric time so for one, guys don't want to be vilanized for having fun o we let ourselves slide. Another thing I heard is that it goes deep into history for the reason that a girl can only get pregnate once every 9 months while a guy can get a girl pregnae every day. I heard that these types of thinking came out in ancint times when it was seen as unnecasary for girls to have where nothing could come from it and guys were ok because they could get a girl preggers anyway.