Well there is an actual real reason for this and it is much simpler than you think. Females have smoother and finer facial structure than men. When it comes to sculpting it is EXTREMELY hard for a sculptor to capture the smooth fine details of a female face. Men on the other hand have much stronger facial features like cheeks, jawline, facial hair, forehead ridges, deeper set eyes, ect... that allow a sculptor to capture the likeness of a man much easier. I have a degree in art and, trust me, capturing a female face in any medium is not the easiest... Sculpting , painting, whatever. IF you can do it well then props to you out there in the artist world. Faces were the bane of my art life so I studied photography as one of my majors.

They aren't even really doing the guys' faces right. They look more like Mark Hamill and Harrison Ford's stunt doubles. I think they're great toys, but the faces all leave much to be desired.
Yeah I sketch and female faces are more challenging to get down than male, pretty much for your given reasons. If you try adding too much detail then it just makes them look dirty, whereas on a guy extra detail makes him look nasty, butch, or chiseled.