Dent's death led to the Dent act which lead to all the criminals being thrown into Blackgate Prison. The Joker destroyed the three mob families in the previous movie. There wasn't really any need for Gotham to have Batman or Batman to be Batman until Bane and his goons surfaced.
"a broke billionaire with no money no Alfred and no nothing is going to be able to get from a land of huts to Gotham and magically show up right where Selina Kyle is without giving me SOME explanation."
The same thing happened in the first movie, however Begins despite being grounded was always fantasy and still comic booky. Just look at the stuff with Scarecrow or the scene where Batman attracts the bats. It had a secret society of ninjas/assassins being trained in the Himalayas . However The Dark Knight abandoned all of that. The fantasy and "comicbooky" stuff was dropped for hyper-realism and to make it a crime/drama. Look at what was stripped from The Joker. Look at how Gotham becomes another regular American City. He sort of tried to bring it(fantasy elements) back in the third but people weren't going to have after what he did with The Dark Knight.
Nah I gotta disagree breh. Dent act got rid of all organized crime, they say that very clearly. That doesn't mean the city was free of crime period in 8 years and Batman didn't just go into business to wipe out organized crime, but all types of crime. To say Batman is only worried about organized crime is kinda short sighted
And in Batman Begins, he was off training with the league of shadows and then a plane showed up to pick him up (although there is still some question as to how he arranged that but whatever) the point is, he gave logical answers for the choices he made in the script and as a filmmaker not just throwing stuff out there to see what stuck