New Orleanian here - the areas in the article are generally on top of swampland and structures sink/erode quite substantially. They’re also outside of the levee protection zone which are primarily earthen levees. When following the road all the way to the end[0] roughly halfway it’s a real trip when you pass the massive concrete structure with a flood gate and suddenly see water bordering each side of the road. It’s also quite dystopian the amount of giant oil facilities that you pass by.

There are non-earthen levees in the city as well. For instance in the 9th ward. These are the levees that failed during Katrina. It’s the Army Corps of Engineers that constructs these levees and have become more complex (better?) over time; imagine an upside-down “T” structure buried in the ground.

If I had to guess, I suppose the reason may be that it’s because they’re outside the protection zone, and so, when it floods (not if) their infrastructure would be surrounded regardless. Also, a concrete structure surrounding only their plant I assume is orders of magnitude cheaper than moving the amount of earth it would take to build 100+ miles of earthen levees.

[0]: https://commons.wikimedia.org/wiki/File:Venice,_Southernmost...