From an article in the Guardian.

Young women scientists leave academia in far greater numbers than men for three reasons. During their time as PhD candidates, large numbers of women conclude that (i) the characteristics of academic careers are unappealing, (ii) the impediments they will encounter are disproportionate, and (iii) the sacrifices they will have to make are great…

Women more than men see great sacrifice as a prerequisite for success in academia. This comes in part from their perception of women who have succeeded, from the nature of the available role models. Successful female professors are perceived by female PhD candidates as displaying masculine characteristics, such as aggression and competitiveness, and they were often childless.

As if all this were not enough, women PhD candidates had one experience that men never have. They were told that they would encounter problems along the way simply because they are women. They are told, in other words, that their gender will work against them.

So, outright sexism and a hostile work environment are pushing women out of academia. Nice.