Novice researchers often enter behavioral psychology convinced of the blank slate thesis. They believe that little boys and girls are born tabula rasa. Parents, teachers, and society then proceed to mold children’s interests, talents, and temperaments towards the dominant gender stereotypes.
Tenured faculty members have a word for blank slate proponents: “childless.”
In other words, men and women (on the whole and in the main) are physically, intellectually, and emotionally different. Thus, you don't need "the prejudice of sexism" to explain disparities. All you need is differing internal motivations, preferences, and interests. Yes, at the tail ends of the distributions you may find overlap, but if the significant majority show similarities to the rest of their sex, then even a small set of sex-based differences can lead to widely divergent outcomes between sexes.
But that gives Social Justice Commissars a lot less to work with, so of course it must be a result only of sexism. (/me rolls eyes)