Although urban areas versus the countryside explains some of this, it can't be the whole picture. Because it's not cities or large towns in general; it's mainly bloody London. Glaswegians and Mancunians and Durhamites and Yorkers and Belfasters (Belfastians? Belfishers?) will happily chat with each other. Not as much as people in the countryside, no, but a hell of a lot more than bloody Londoners.