It all comes down to statistical distribution, and men having a wider range of attribute distribution, so they are more likely to have the best* leadership traits. If you take the top 10 leaders in a tribal society with 150 members then quite a few will be women and they will be the leaders. The leadership positions don't scale linearly though, in a city of 10,000 people you might only need the same 10 best leaders but now most/all of them will be men.

*Best: the best traits to become and remain leaders, a selection quality not a value based one. Being narcissistic might make someone the best in this sense.