Look closely at a female reptile, a female amphibian, a female bird, a female fish, a female insect, or most non-primate mammals. You'll doubtless notice the lack of a particular characteristic that is common to female humans. If the character is an alien or artificial life form, then it makes a little bit more sense. Aliens have Bizarre Alien Biology after all, and creators of synthoids and such would probably want their "children" to be anthropomorphic enough to fit in. Not to mention that it's easier to design a skin-tight rubber bodysuit with strange textures for use by human actors.