The Somerset levels are a special case whereby, as in Holland, water was pumped out of swampland for decades and the soil shrank, leaving useable farmland but at a cost of it being a few metres below sea level.
I'm sure we have the engineering know-how to build houses on stilts or on bouyant foundation platforms but anything which eats into a developer's profit margins just isn't going to be built. Carpets, furnishing, kitchens and home entertainment installations are deemed to be replaceable, so insurance customers must bear this burden, instead of them.
Housing development is only a big thing because interest rates are artificially being held low and other growth opportunities are either too weak, too abroad, or higher risk, so I also blame the BofE for shaping our economy in such a way as to make the flood plains into a cashcow.