FEMA Revisited

Read this reasonable piece about FEMA and natural disasters but ponder a simple question;  why do areas affected by natural disasters receive any transfers at all from other regions?  National defense is a public good but how is natural disaster insurance a public good?  You can convince me that the state that is impacted can provide disaster relief to the affected community but why are federal funds used for this cause?  When I buy dinner, I use my own funds to pay for the dinner.   Why don't I ask other tax payers to buy me dinner?   Yes, it is true that dinner is a nightly anticipated event but why don't states at greater risk for disasters keep their own "rainy day" fund?  If they don't keep such a fund, why should other states "bail them out"?  If no private insurance company will provide market insurance for those taking risks, why should the government implicitly provide that insurance through ex-post payoffs?  What risks do we subsidize and what risk taking do we tax?