It isn't. There is Baton Rouge, Louisiana (ever heard of it?), plus over a dozen oil refineries, including two half a million barrel per day operations, one of which, Exxon-Mobil Baton Rouge, LA is the largest oil refinery in the US, and is where the cat-cracking (catylic cracking) method of refining oil in to gasoline was invented, creating more gasoline from a barrel of oil. This country would be in a world of hurt, (you included) if these refineries were flooded. Finally, this was not an easy decision to make. Days went by while this was being discussed, unlike the sneak night decision to blow up the levee upriver.
Thank you for your intelligent post. The number of posters here who seem to believe that LA is just NOLA is astonishing. Geography lesson, anyone?