I live on the shoulder of a hill, and my view is much better than that in the flood plain below. Houses in this town are in big demand from outsiders. On the lower ground, they are closer to shops, and schools, and major roads etc. Houses there are attractive, and they must be safe, because only an idiot would give planning permission to build on land prone to flooding, surely? Incomprehensibly, flooding is "not a planning issue", nor are overloaded waste water or sewage facilities. If the water utility, or Environment Agency fail to raise any issues at the outline planning stage, they carry no liability (The Thames Water v Bromley judgment may alter this, it's a bit early to say.)
The simple fact is that the odd freak event (like an underground stream bursting through the side of a hill) would barely affect the premiums. It's the building of large estates on flood plains that cause the problem. That is happening because the builders love the nice flat land to build on, and planning law is daft enough to allow it.