To add to the other explanations, there are Herr Doktors that think so high of themselves that they put the title everywhere, business cards, emails addresses, name on the letter box, and everywhere else they are supposed to write the name, you even get to write it on personal data online forms.
Coming from a country (Portugal) where having an Engineering degree still has a similar connotation and there are still some that make the point to be called Eng. SoAndSo, specially on smaller towns and villages, it was kind of ironic to find a society where it is taken to the next level.