You are neglecting the negative effect of what people have to pay out of their own pockets. Even for those with insurance, there is going to be a reasonably large deductible. Add to that the utterly devastating effect upon people who don’t have insurance. Whether they should have had insurance or not is beside the point - the point is that these people will have debts for the rest of their lives (particularly those who live under the jurisdiction of a homeowners association that requires a destroyed property to be replaced before it can be sold). Their purchasing power in the future will be vastly reduced from what it would have otherwise been - either that, or their credit will be ruined, which will negatively affect their ability to spend money in the future. Many people will never recover.
It is an economic fallacy to believe that something like this is stimulative. Of course it is for people who did not lose anything. But a blanket statement like that completely ignores those who have lost. It also ignores the effect upon insurance premiums at least in the affected region, if not nationwide. Those premiums will rise in order to both replace the money that insurance companies will pay out, and to mitigate the risk of further claims of this type. Those increased premiums will reduce purchasing power across the nation. How is that positive for the economy?
Poor people don’t usually own their homes. They are usually renting, which means the cost to rebuild with fall on the owner or more specifically their insurance company.
Nearly no one owns their home outright, which means they are required to have insurance and if they are in a flood zone, they will be required to have flood insurance.