Why aren't people moving???

People who live in the big flood areas know that every year theres always a big problem with floods. Why don't they move or get ready for the floods? I know some people do get their homes and self ready for the floods but some people don't. Knowing that the water some times gets really bad that it can mess up your house. I don't get it. What is it that they don't move? Is it that they have some kind of connection with the home or don't have the money?...or what? Personally I would think of moving to some where far from the flood areas
~autumn