This just means that the coasts are far more racist, segregated, and insular than "flyover country" where the rich co-exist in the same neighborhoods and zip codes with the middle class. Rich coasty Democrats like to live an incestuous lifestyle where they interact only with other rich Democrats in a mutual admiration society. Rich heartland Republicans like to live a more diverse cosmopolitan lifestyle embracing all cultures and payscales not just those of the sneering snobbery class.
If you lived in some of these cities (e.g., Filthadelphia and Baltimore), you would want to be segregated and insulated from the 'man in the street'!
You're kidding, right? Ever been to Naples, Florida or Bloomfied Hills, Michigan?