^Again, I think the writers' actual record proves that they are more than capable of writing women as more than just eye candy. Evidently you haven't seen the shows and movies I referenced: I have, and I guarantee, the female leads were very strong and central to all of them. So you're absolutely wrong to accuse Abrams, Kurtzman, and Orci of sexism.
And I gave you a plausible reason -- pressure from the studio to conform to the target demographic. Surely you're aware that the creators of film and TV are not given total creative freedom, that they have to conform to the wishes of the studio or network executives. A lot of the decisions that shape films and TV shows are made by the executives whose names we don't see rather than the writers, directors, and producers whose names we do see.