In games that have gender based perks, like Agent of Dibella in Skyrim or LadyKiller/Black Widow in the Fallout games tend to be stronger for female characters because more of the NPC's are male. This is more adding another reason than claiming that it's the main reason. I don't exclusively play either male or female but typically when I play a female character it's because I'm building a character that is less physically aggressive. I know this is playing into stereotypes but sword and board tends to be male while stealth archer tends to be female.