Because our society doesn't have the stomach to just wash our hands and say we're not our brother's keeper. Inevitably, people who don't leave will later call for help and risk others if things get too bad.
It's like how we are idiots for not letting people die in the streets if they don't buy health insurance.
My brain is fuzzy on the details, but during last year's storms, I remember some official saying something like, get out now, but if you choose to stay, don't call for help because we are not going to risk our lives to come and get you.
I don't recall whether anyone did stay, later called for help, but was refused. Seems to me if that did happen and people died as a result , there would be all kinds of lawsuits.
But it is that kind of tough stance, I wish we would see more of. It should not be up to government to save people if they don't evacuate and later get into trouble. The problem is we have too many people depending on government to save them from their own folly.