"Correlation does not imply causation". The go-to of the armchair scientist. It doesn't imply there isn't causation, either.

We have plenty of evidence of rampant systemic sexism. We have plenty of evidence that women left the field due to that sexism. We have evidence that the field's composition changed fairly recently (in the late eighties). We have evidence the culture changed around that same time.

If you would like to make your gender-essentialist case, you should at least try to build a model that explains these things, instead of asking empty rhetorical questions.

Most importantly, I suggest staying in the industry we're discussing, as opposed to bringing up straw men outside of it.