Neat and tidy

The reason that a perfect gender binary never truly existed is simple: humans are exceedingly complex creatures. The imposition of the binary was due to religious and social structures which required obedience. Hence anomalies both of sexual and behavioral nature were seen as abominations to be remedied. This meant intersex people were "repaired", transgender people forced to comply and all behavioral expression outside the accepted norm was shunned.

Today that is changing but it is grating against the dogmatic ideas of those groups who rest their foundation on the veracity of this model. Never mind that nature is replete with anomalies, human beings are, according to them, apparently immune to them. In the last decades pseudoscience has even been invented in an attempt to put the genie back in the bottle thankfully to no avail.

Pity that ignorance and stupidity are also permanent fixtures in humans.