Eric Holder was asking for it...

"I want to speak directly to [Co-creator Ed] Burns and Mr. Simon: Do another season of The Wire," said as the audience laughed and applauded."That's actually at a minimum. ... If you don't do a season, do a movie. We've done HBO movies, this is a series that deserves a movie. I want another season or I want a movie. I have a lot of power Mr. Burns and Mr. Simon." 

...and David Simon gave it to him:

The Attorney-General's kind remarks are noted and appreciated. I've spoken to Ed Burns and we are prepared to go to work on season six of The Wire if the Department of Justice is equally ready to reconsider and address its continuing prosecution of our misguided, destructive and dehumanising drug prohibition.