Closer you get to the city center in New Orleans, the less helmets you will see. Besides the style points, and the expense (folks spend all of their helmet money on beer), I find that people who ride bikes for utilitarian purpose do not wear helmets as much. Just like jumping into a car and going to the corner store. A helmet in the car might very well be a good idea, but unless you are RACING your car, maybe not all that necessary.
I always wear a helmet, but I always ride like a jack*****. It holds my rear-view mirror nicely and keeps the sun off my scalp (mostly). Maybe if I ever rode carefully, I would feel differently. My helmet is a Bell Metropolis. Got a Gore-tex cover and zero style points. I don't care what anyone thinks about it, and I sure don't care what they wear or don't wear.
But it is interesting that people who live on their bikes often do not wear helmets, even in congested cities.