New Orleans area after Katrina needed new schools, firehouses, police stations, levees, roads, bridges, government offices, sewer systems, hospitals, pumping stations, nursing homes and parks just to mention what comes to mind. The power grid was almost completely destroyed. Much of this was built or rebuilt with either grants or matching funds from the federal government. SBA loans and grants to rebuild homes and businesses. Billions where spent to rebuild the Gulf Coast. Federal money is still being spent to upgrade damaged infrastructure. I just don't see the US footing the bill to rebuild in the Caribbean.
Losing a home to a tornado is a terrible thing but it is localized. Normalcy exists a couple of miles away. Can you imagine the scope of destruction from Katrina? I had to drive 2 hours to Baton Rouge to get gas for the generator. 3 months to get power.
Add to that the assistance Houston and Florida needs?