Main reason is because when drawing women; you wanna draw less. The more you add the more masculine they become.( This is okay if you want to portray a more muscular woman.) All the forms are there, just simplified more. That's why when starting out, students are told to draw more men for study than women. On a male model, you can draw as much forms and muscles as you want, and you can get away with it ( Usually makes them feel more powerful ). When drawing a female model, especially when they get in a graceful pose, the more details you add the less graceful it feels. More details also slow down the flow of the eye. ( Which you must learn to use to your advantage)
We always joke around when teaching how to draw heads. If you drew all the forms on a woman's face for a portrait on the job; you'd get fired. Usually the more you add, the more aged or masculine she gets. Anime is a good example of this. Due to the fact that the faces are so simple, everyone looks young. When they need an older character, they just add a few more details to age them. It's a very simple and effective way of portraying age.
But what about the thighs? I still don't get how their's is different from men. I'm guessing where the obliques of men overlap their something(I dunno what that thing is under the obliques is called) a woman's just goes outwards.
Woman have to a wider pelvis because they have to give birth. Also woman and men develop fat differently. Men develop fat around the midsection while women develop more fat around the hips and thighs.
All the muscles are there just on a different frame. Men and women both have external obliques. Women and men don't have different muscles.
To recap. The hips thigh area on women look wider because it's generally wider. Default hip shape for men are cylinders, women more of a lamp shade. Men tend to be a V shape and women a V shape with the opening pointing down.