I think it is because girls mature emotionally a lot sooner than boys. Most boys didn’t start digging in and grinding like the girls did until maybe junior year of college. I wouldn’t be surprised if mentally they were years apart in highschool.
Now today we have a society that is no longer so biased in terms of opportunities along gender lines. And what do you know, girls are generally eating boys lunch here. They are outnumbering them in college. They have higher GPAs. They are starting to outnumber them in post grad programs. And eventually in the workforce this will happen as well, as this cohort gets jobs and supersedes older male dominated cohorts from before the silent cultural revolution over the last 30 years.
Eventually we should see this effect find an equilibrium where the number of women in high impact jobs vs men reflects the underlying intelligence bias women have over men.