re: The Dark Knight trilogy question

Unlike previous incarnations of Batman, the Christopher Nolan version of the Caped Crusader seemed to concentrate much of his time and effort on organized crime. Petty crime is going to happen no matter how hard you work to stop it, but organized crime is a disease that can be treated and cured. You eliminate organized crime from a city as bad as Gotham and you will be going a long way in reducing that city's crime rate by a substantial percentage.

Maroni and the Chechen, the two most powerful mob bosses in the city, were both dead by the end of the events in The Dark Knight. The Joker had been apprehended by the police. There was very little for Batman to do but run and hide by that point.