I don't know if I agree with Mark's reasoning or not, but you can't over-state how difficult it is (politically) to accomplish anything here. Especially things that are expensive. Logic has no seat at the table.

This country is young (relative to Europe and elsewhere), but people have built in stupid places, for stupid reasons, and have too much invested to walk away.

There have been major construction projects (freeway system, reservoirs, etc.) which have required major changes to extremely large areas, but not in a very long time (pushing 75 years?). And, it's usually the little guy who loses his house, for pennies on the dollar.