Probably because the storm passed through the rest of the Gulf Coast, and people could return quickly. Might not have been much to return for, but New Orleans was closed for a month, and about a half million people were displaced (the entire population of NO). Even then, it was a month before power was turned back on, and that was only in unflooded neighborhoods. It was about 5 weeks for my mom's house.
Oh, there was the Superdome/Convention Center thing on TV for several days.
Lee