Why is it taking so long to improve sewage treatment?

Commenting on "Outdated Sewage Treatment is Suffocating Fish in Puget Sound," published Dec. 8, 2020, Harry Branch writes: 

The article on the "pressing state of environmental decay in Puget Sound" causes one to wonder. Why is it taking so long to improve sewage treatment? Several other thoughts come to mind as well.

1. Nitrates travel 18 times farther in a buried pipe than one that sees daylight. This is because phytoplankton that digest nitrates can't live in darkness. They're tiny plants.
2. Phytoplankton are also one of the world's greatest suppliers of available oxygen. To increase oxygen and reduce nitrogen we need plankton and they don't grow in underground pipes. Olympia sits on 160 miles of stream-in-a-pipe.
3. These processes are especially significant in estuaries and all the major stream estuaries in Olympia are in culverts. High tide goes up the pipe. These are places where zooplankton need to get mixed into the system to control overproduction. If the structure is there we have the start of the food web. If not we have a septic tank.
4. Salt marsh, tide flats and other estuarine features are also big players. We continue to keep them in a degraded state with real estate developments in the worst possible locations.

Think physical (shape, structure), chemical (dissolved oxygen and nitrogen) and biological (plankton) parameters. These things don't exist in isolation.