This is going to go over like a lead balloon, but I think it began when Women's Studies became a thing in colleges and universities.

Back in the day the various movements were to break free of divisions ("boxes"). Sex, sexual orientation, race were to be just (one) factor, though major shaping one, in who a person/member of society was, not a means of oppression. Academic focus on these boxes was highlighting and stressing the divisions rather than acknowledging them and accepting and developing the individual. Reactions to these concentrated studies did hint at the problems ahead IMO. Even in elderly, conservative areas, change was beginning to happen, but activism and awareness is hard, tiring, and time consuming. Also, it wasn't happening fast enough for some, and the indications that it Could happen scared others into having to put a stop to it. These two forces used each other to thwart the ideal.

And having seen the blocking strategy be sucessful, used today to further control women, it's moved down into elementary schools, even. (I'm talking the transgender narrative now)