Sure they change, but we are discussing here why, how, and by whom. Not a conspiracy (as it implies something clandestine), but a result of a deliberate, concerted, public effort by numerous groups that can be loosely combined into "left-wing" (PC nuts, feminists, progressives, liberals, loony left, etc.)
This is ridiculous. Where did you get this idea from - Glenn Beck?
Thanks to advances in science, we now have a much better idea about the biological basis of sex in mammals, including human beings, than we did a century ago. To take one example at random: we now know that some female athletes have physical attributes we normally associate with being male that give them a performance advantage on the track. That's to do with sex. That's biological. We also have a better idea of cultural diversity and what it entails than a century ago too. When a male does
penile subincision, he's doing because his culture tells him it's a good thing to do. His sex is male but the way he understands how to be a proper man (his gender role) is different from you and me.
In short, in working through things like this, last century researchers found it helpful to distinguish sex from gender. Nowadays we take it for granted that sex and gender are as different as biology and culture, simply because it makes so much sense.
Finally, most of the people who did this primary research were neither women nor feminists, because as we all know, women in almost all countries had their access to practicing science curtailed until not that many generations ago.