Because they changed the genders for the same reason they cast a black guy as Johnny Storm in the Fantastic Four reboot. Only difference is this is gender instead of ethnic diversity bullshit designed to please the SJW/PC crap that has been going around mostly America recently. I mean let's face it we can't even have a movie poster of Mystique being strangled yet in the movie she kills/strangles a fuckton of people because of the SJW/PC crowd. Also from what I've seen so far the movie looks like shit and is trying too hard to be better than the original which it won't be.