In "Why do so many incompetent men become leaders" Thomas Chamorro-Premuszic argues that this trend is primarily the result of male leaders confusing confidence for competence. What causes leaders to be effective is humility not hubris.
"There is now compelling scientific evidence for the notion that women are more likely to adopt more effective leadership strategies than do men. Most notably, in a comprehensive review of studies, Alice Eagly and colleagues showed that female managers are more likely to elicit respect and pride from their followers, communicate their vision effectively, empower and mentor subordinates, and approach problem-solving in a more flexible and creative way (all characteristics of “transformational leadership”), as well as fairly reward direct reports. In contrast, male managers are statistically less likely to bond or connect with their subordinates, and they are relatively more inept at rewarding them for their actual performance. Although these findings may reflect a sampling bias that requires women to be more qualified and competent than men in order to be chosen as leaders, there is no way of really knowing until this bias is eliminated."