There doesn't seem to be any point in rebuilding. For what? The hope that another Katrina doesn't come around for awhile?
Pompeii?
Not a very useful common, specially at this point where survivors are still being rescued.
The Dutch, particularly, can give you lots of reasons why that simply won't happen. Ever seen the documentary of their "big flood"?
In addition to where would they go, the connection to the land for generations makes it totally unlikely that everyone would want to just give up and move.
Human nature.
Natural disasters can happen anywhere. Should everyone just move inland 20 miles? Get away from the earthquake-prone areas? How about the midwest with tornadoes? We just rebuild - it's all we can do.