The gender equality is one of the few exceptions from the medieval atmosphere. Asking "why are women equal to men in BM" or anything resembling that question is much akin to asking "why are you supposed to throw the ball into the basket in basketball" (Using rough terminology here. Besides it really was a basket originally).
The answer: Because probably very early in the development, very likely even before public release, this guy named Tom Vogt decided that, similarly to why religions should not resemble real life religions too closely. They are decisions meant to be considerate to the players, as some people may be sensitive to topics like gender and religion.
Now before someone goes to me and says "But this is the Background section, we're supposed to discuss the Background!", I'll concede that such an observation is quite correct. And yes, men were pretty much the ones fighting, leading, making money, and so on. That's great, and have fun talking about that. But that doesn't hold in trying to enforce it in the game, one in which almost every player has been raised in an environment with little or no gender discrimination.
