It's not just about denying nature, but denying all the choices along the way by so many parties. You see something like, Company XYZ hires 2/3's men for something. They are called sexist, the people working there are sexist, it is a hostile work environment, etc... and it's the 2/3's number that is offered as "proof".

Further, just proposing that nature is the cause can get a person fired.

My stance is that lack of proof is being met with lack of proof by a group that is tired of being the target of constant accusations.