On the surface, it can be believed that it should be the resident's right to stay in their home in the face of coastal flooding. In reality that answer is way to selfish. Law enforcement is required to respond to calls of emergency. It is unethical for society to force them to respond to a coastal resident in the midst of a flood that they knew was coming because they are to selfish to leave. This is why these locations should be evacuated.
The threat of coastal flooding has been around for a long time, and yet coastal cities still exist. Flooding does not happen spontaneously; there is usually a fair amount of warning that precedes any flooding that may happen. Evacuating cities before these warnings happen is fairly silly, as coastal cities offer benefits that inland cities do not have.