I think the gutting of middle America is a big part of it. The most talented people are forced to leave for the coasts to make the most of their capabilities. This hurts both the leavers (like me) who have to built roots from scratch in their new home and hurts the remaining population due to the resulting brain drain. The us-versus-them attitude is then worsened by classist attitudes toward those entire areas based on the population who remain by my fellow “progressives” who will endlessly mock “flyover states” and anybody in them.