We have voluminous statistical evidence that women are judged more harshly than men in all phases of hiring when the only differentiator is being perceived as a woman. That's not handwaving, that's decades of study. Handwaving is "for whatever (social/biological/cultural) reason".

We know there's a pipeline problem, and we are fighting that. We don't think it's going to be solved overnight either, and critically, not just by addressing the pipeline because, as numerous stories from the tech industry have made clear recently, even when qualified women make it through that anemic pipeline, they still face individual and institutional sexism. Or have you forgotten that one of Uber's recent departures left Google after an internal sexual harassment scandal that was quietly handled?