They either didn't or just didn't want to enact it. It's been known that if NO was ever going to be hit, they would need to start evacuating 72 hours before it hits or at least 10,000 would perish. Now here they are in this mess, with highways starting to jam, people in shelters without food, water, electricity, with 20+ feet of filthy water outside the door, not to mention the rest of the devastation.
Snakes, Alligators and fire ant mats are going to be everywhere, too. Very unplesant, those fire ant mats. When one of them grabs you, you have an entire ant colony climbing your body all at once. They float on top of the flood waters like little rafts.