Often though, the municipality that causes the flooding is not the one that experiences the flooding:

Suburban sprawl paves the field that used to absorb storm water and runoff, channelling water into culverts, sewers, and drainage in higher volumes, and in much shorter times that what occurred before. Older communities located downstream were built well before the present size and scale of rural subdivisions, and are taken by surprise when even moderate storms result in flooding, but arguably this is not the fault of the communities where flooding occurs. 

And why don't residents move? Because that is where the roads are; that is where services are. To relocate flood victims is to pave more farmland, potentially contributing to more flood damage in the future.