It is true that the gender imbalance in gaming has mostly smoothed out, but until that happened the software industry already turned mostly male. And even if nobody intends to erect barriers, in a group that's heavily skewed towards one demographic everything starts to cater towards that demographic, pushing everyone else away. So unsettling the balance once for long enough may be enough to explain where we are today.
>Finally, what is your explanation for the huge increase in the proportion of women in biology?
I honestly have no idea.