How do you know there aren't? I mean have you seen the giants? They could be male or female and we just can't tell.
It's like this in many games... lol, creating a female model for every mob creature takes up unnecessary developer time that could be allocated effectively elsewhere.
I imagine that like booby-taunt (wonder how many players remember booby taunt?) booby smash would be an overpowering ability for giants, so safer just to have men. The women are put away in secret places because their beauty (like the ancient legends of the High Ogre women) is too astounding to be put into pixels.
They mate with very women of other races, and always produce male offspring and the giant trait is domanit. That or they reproduce asexually, like the brides of wow human male or orc characters.
