Border towns in Texas and Arizona are seeing ten thousand or more illegal immigrants per day. We can’t leave them all there or they will starve. If we can’t deport them then we must spread them around. Personally I am more in favor of deporting them (after all, by our standards they have committed a felony), but as long as we have sanctuary states to send them to then surely that is just as good.
The sea isn't like that. Everyone who's bought property in Florida in the past decades knew what's happening, and it's clear that Florida will need expensive new infrastructure to supply those properties with freshwater fairly soon. Who is going to pay for that? Florida's behaviour towards Massachusetts today influences what the voters' answer will be when Florida asks the rest of the union for help with that water.
Someone whose land is going to be submerged by the sea in maybe twenty years, and who's going to ask for expensive help to keep that land livable for those few years, needs to show solidarity. To flaunt solidarity.