Surely there is a study here for a graduate student in sociology or possibly anthropology. Was equal distribution of space important when we lived in caves? Is this a leftover behavior from lizards sharing a den?
Along with pressing the up, down, or floor buttons when they have clearly already been pressed this is another seemingly inexplicable elevator behavior. I find it oddly irritating. Sometimes I have the almost irresistible urge to scream "WAKE UP."