In addition to what leereves mentions, preferences could be different because of biology also in a different way. Knowing that their child-bearing period is quite limited, women rationally overweight "having children" and underweight "having a great career" in their youth, compared to men, who can work their ass off for 20 years, and still easily have kids afterwards. On other words, it's easier for men to "have it all" than for women (I don't agree with the values expressed by this saying, but I'm guessing many people do).
