You have been waiting for me to tell you  something insightful from psychology  about the use of stereotypes and the perpetuation of clichés.  You think that there are two motivations, though you might not have the data or the vocabulary for them, and your intuition is mostly right.  Psychologists who study social cognition (mental processes that support thinking about the social world) for years characterized humans as “cognitive misers.”  This means, of course, that people want to think as simply as possible so that they have time to do other stuff with their minds, like play computer games and figure out how to work their iPad (will someone please help me with this?).  It’s true.  There is so much to think about that reducing the need to think per se is a mental state desired by many.