As for property developers, I'm sure they're not forcing anyone to buy the houses they build, either in the US or the UK.

Of course not - but I'll bet few of the people who bought houses around the towns in Sussex ever thought they'd be susceptible to severe flooding. "Safe as houses" eh? It's the long-term planning on the part of local authorities that's at fault. If you consistently allow known flood plains to be developed by companies who, in the end, are only interested in selling houses, then the environment is changed for ever.