Why do are female celebrities more pressured to be "y"?

OMG! i know.. i agree with you 100%! I am a HUGE Hilary Duff fan and i was SHOCKED when i saw a clip of War Inc on the tv.. i was like "That can not be Hilary!" she would never dress like that.. but it was.. and its awkward that her character is an "over ed" pop star.. she never did a "R" rated film before.. it's going to be weird for me because i'm so used to her being in PG or G movies.. lol