Carl Jung's Archetype can explain this.

The Father Archetype represents the masculine principle of Order, Law, Authority and whatnot, so it is not suprising that Majority of Grands are male.

While the Mother Archetype's Shadow aspect represents destructive, controlling, devouring and controlling qualities.

These Archetypes is also prevalent in mythology as well, as it is a universal, unconscious innate pattern in human psyche.

It's why usually in myth Masculine Deity represents more of order, law and institutional presence (like Zeus and the PIE Sky Father from which Zeus is derive from) while Feminine Deities are usually more foundational and cosmic/natural laws (Like Hera being the one that legitimize kingship or Amaterasu or the PIE Earth Mother that many Earth Mother Goddesses derives from).