Why was New Orleans built below sea level? That's just plain stupid.

Location is more critical than elevation. Consider the strategic military
value of being the last town on the river that reaches the entire middle
US. A little war around 1812 hinged on things like that.

Nawluhns is also the closest thing to the third-world in the US, in terms
of civil engineering, compounded by a corrupt culture. Such character is
not going to prudently invest in infrastructure to withstand such a test as
Katrina.