Bonus fact: Flood Insurance is just a government handout to insurance companies, and isn't actually insurance at all. The company just pays for whatever the customer lost, and rebuilding their home exactly the way it was, and the government writes the insurance company a check for that amount. Think the construction lobby had anything to do with that at all?
The sarcastic answer is because waterfront is the most expensive and desirable real estate there is and the seismic impact of waterfront abandonment on real estate and culture will be more than most municipalities can handle. The real answer is that rich people live on the water and they vote.
This is still in its infancy and needs tons of looking into, but I know that there is theoretically a way to build lintestone with our CO2 emissions and calcium rich water. Perhaps some structure can be slowly built with this is mind.