I think populations concentrating to cities during the past +- 30 years has also changed peoples ways of self expression. Still today, in the country side peoples wordings and attitude in their expression is much less self centered and "self enhancing" than in the cities. That's especially obvious regarding teenagers, and the habits usually stick.
In the competitive circumstances of the cities people are underlining (or feel they should) themselves all the time, they are like gorillas who feel they have to continuously drum their chests. The ways to do it are more subtle, though. And the ones who are not "alphas" develop all these stressfull, verbal neurosis (subconciously) struggling to maintain their street credibility.
In Finland we have, for example, a "Helsinki-S" , a certain type of very sibilant S, which is regarded pretencious and cocky. It's looked down upon in the rest of the country, and, by many, in the capital as well.