For some the use of the first name assumes a familiarity which probably does not exist. The universal rule is that appropriate levels of interaction are both accepted and used in common parlance by everyone. Thus it's rare for a speaker at a press conference to be addressed by their first name though the speaker might well respond using a first name if they know the journalist. 'Anthony, how did your chat with Sergey (Lavrov) go?' is not something we're likely to hear. Of course it's down to preferences with ordinary conversations as in 'please call me Joe' or whatever.
First name informality has been a feature of American culture since before its founding. We use a more formal protocol for official business. It seems controlling to insist against common practice that normal persons treat one with this kind of formality.
