Flood defenses protect cities, not rural houses. But this is inevitable.

When a lot of people live in a small area, a small perimeter can protect them all. Where this approach can work, it is efficient use of public funds.

By contrast, protecting houses lying sparsely on the ground would be far more expensive per person protected. That is not feasible. The efficient thing to do for the people who live in those houses is to buy them out so they can move to places that are safer.