The problem is that playable female sprites exist only for medium size characters. That was all the devs had time to do, in their race to finish the game before they got shut down.
If those sprites existed in the game code, even in raw form, someone like Drog Blacktooth (the creator of the UAP) would have uncovered them by now. So, adding them at this point would entail actually drawing and animating the sprites, modifying the code to allow for females of other races, and associating those new female characters with the relevant (and possibly some brand new) dialog trees.
Still, could you imagine a half-ogress trying to seduce Willoughsby in order to complete a quest? Or Raven falling in love with a woman half (or twice) her size? Or Ogdin's stunned reaction upon meeting his first female of his own race? Or poor Magnus's confusion when he learns that "Dwarven women never leave their caves" is yet another discredited myth from that godawful book he had the misfortune to take to heart?
Ah, the possibilities are endless.