re: Why did NOLA expand North and not West?

Swamps. You've got what's now called the LaBranche Wetlands and the Bonnet Carré Spillway west of Kenner. You've got what's now called the Bayou Sauvage National Wildlife Refuge in the east. You've got the Mississippi River to the south. And lots and lots of the areas around all of those are swamps, or at least historically were swamps, flooded, and were / are difficult to build well on.