Because even in all of our infinate wisdom and technology, we still can't fool mother nature. It will happen some day, it's just a matter of how long it takes. Hopefully when that day comes, enough people will have left so as to minimize the losses...
The only way to solve the problem completely would be to pick up the whole city and move it to another location outside the natural basin it was built in. Unfortunately, when Iberville and Bienville planned the city, they knew very little about the physical geography of the area, much less about hurricanes, storm surges, drainage, etc. Did you know that New Orleans didn't have sub-surface drainage until the 1880's?
It's interesting you should mention that... I read somewhere that the reason New Orleans is where it is was because the land originally was his (Bienville), and he wanted the city there. In order to get it started there, he convinced the "powers that be" that the site was the first "high ground" comming up the Mississippi from the gulf, knowing it wasn't... Even then, it was Louisiana politics at it's finest...
