It's because women get pregnant (and in general they also care about their kids). All of a sudden you have to stop work for a year, and afterwards you need to dedicate time to your children. THIS is the main reason why women don't get into important roles. They can't dedicate their whole life to work.

The second reason is sexism. "Diversity hires" is bullshit now, but it was originally implemented precisely because most employers prefer to hire a man than a woman.

Just a couple years ago, a prestigious university of medicine in Japan was discovered to alter the results of the entrance tests so that women would fail and men would pass. Imagine how long this went on? Women passing the entrance test but being denied access and being told they failed; men not passing the test but getting access. And of course I bet people were saying "women just aren't interested in medicine".