This is why NO has survived almost 300 years. It certainly wasn't because the climate was so healthful! But the nation NEEDS the port. And there will be a city there because of trade (like many important cities in bad places, trade talks, health walks.) Houston nor Mobile can carry it all.
Some day, maybe, when the Old river controls give way and the mississippi sends most of its water down the Achafalaya, then the rebuilt Morgan City might the the city that's essential. But right now, its the river and its nexus of trade that make New Orleans needful.
Brings up the question of why we only have one deep water oil port in the Gulf.