> Protecting a building that has a lifespan of less than 100 years against an event with a probability of occurring between .005 to .002 (the 200-year to 500-year event) is a hard sell.

Only in America. The Delta Works in the Netherlands are designed for the 2000-year flood. This is the minimum - there are areas that are protected against the 10000-year flood.

This makes sense. It is not normal that densely settled areas are flooded at least once during the human lifespan.