It is not a southern-German thing. Based on personal experience, I can safely say that German has become more informal in the last 20 years. Using _Du_ has become more common, in a way that it feels rude to Siezify people in certain situations. For instance, saying _Sie_ to a waiter under 50 in a café would be considered a little off nowadays. Also, big companies started Duzifying their customers, with IKEA being one of the most prominent examples. While some professors at the university still used their title in written communication with students, a lot dropped it and made a point not to be called "Professorin" or "Professor", some even go by Du and by first name with their students. That would have been beyond imagination 30 or 40 years ago.

Written communication has become more informal, too, coinciding with email having become more widespread and replacing a majority of letters. 20 years ago I learned in school that _Sehr geehrte Damen und Herren_, _Sehr geehrte Frau_ or _Sehr geehrter Herr_ is the go-to greeting in letters, nowadays _Hallo_ is more common, and the old formula comes across as stiff and old fashioned. You would expect to be greeted like this in letters from your bank or from the government, but not from actual people you know in person, such as your landlord, for instance.