Something that tends to happen is that you have lived for so long in a place, that you lose the charm of it. You don't see the things that it has anymore, the wonderful sides and sights. And then one day you leave and miss it. And start seeing the differences with wherever you are now and figure out that the other place was HOME and you can appreciate it. It seems like Billy Joel is seeing everything that New York has to give and forms his own "State of Mind" about it.