I have theories on this.....
. It's a theory I developed re driviing. The sexist stereotype is that women are poorer drivers/more nervous drivers. I actually think that this is true.....
.... but not because of poor little women's brains being incompetent.
It's because of the way (overall - as always, it's not consistently true), women are TAUGHT to drive and the expectations for them. Teenage girls admitting they are scared of driving are likely to get support, accomodations may be made, they may be "let off" certain things. Teenage boys, overall, less so. There's a subtle, but real, expectation that boys will like driving, be good at it, even be TOO enthusiastic and likely to take too many risks.
Baically, societal wide sexism is so engrained it even affects this. Similarly to that research I saw a few years back that said if you ask girls how good they are at maths, even as young as 7, they'll say they're less good, even if objectively they are performing at the same level as the boys.
And I suspect with map reading, it's that same unconsious bias/sexism at play. This idea of "women being bad at navigation" that then infiltrates everything.
My father had zero tolerance for any suggestion that basic skills like map reading or driving were impacted by our sex. His view was that these were important skills and you needed to learn them, and learn them properly like many other core life skills from reading to cooking.