I don't know if it's because of having only one X chromosome, but there are very small differences between men and women on the average and very large differences at the extremes.

Men are a little more aggressive than women. But the top 1% of the most aggressive people are all men (and not something to be proud of either.)

Women are a little more agreeable than men. But the top 1% most agreeable people are almost exclusively women.

So small differences on average can still mean there are large differences at the extremes.