I'm really not the person to talk about styles of address, current or historical. Referring to someone solely by their surname is typically a male-only thing as far as I am aware. I believe that it's especially prevalent in english schools. Women might technically not have an independent right to their names as they would take up their husband's name upon marriage. Being called by one's first name is familiar and in the context of a public figure demeaning. Consider the effect when someone refers to Obama or Trump -- no one needs to disambiguate who these names refer to. We refer to Marissa Mayer because she's not notable enough to simply call her Mayer. That would be my uninformed take on things, at any rate.