Given that reproduction in mammals is inescapably binary, and a really big fraction of social interaction in humans is shaped by courtship, both overt and cover

Given that reproduction in mammals is inescapably binary, and a really big fraction of social interaction in humans is shaped by courtship, both overt and covert, it's hardly surprising that our historical perspective on gender roles has been predominantly binary too. I think another reason "things are different now" is that more of us think abstractly today than in years past. Many of the perspectives and possibilities we entertain today would have been alien to more of us 50 or 100 years ago, when the world was more conventional, more black and white. Finally, with the multitudes of voices that no longer remain hidden behind mainstream media outlets, we're more aware of nontraditional, complex, and nuanced POVs today. That helps us realize that many psychological variations exist "between the lines", not as pathology but as a matter of natural variation.