"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
Well, it's kind of difficult to rebuild anew something under the management of corrupt, thieving politicians and their cronies.
Parasites like them can only survive on a healthy host, and for centuries New Orleans was healthy and thriving as a major port city and commercial hub.
Parasites can't build anything themselves, though, that requires productive, self-reliant, confident people without too many parasites sucking their blood while they build.
Katrina threatened to leave the parasites high and dry, with hardly anyone left in town to graft - they've had to resort to swindling the rest of the United States.
Article: Where Did the Katrina Money Go?