The union of states arrangement has the side effect of putting the states in competition with each other for things like new/expanding businesses and residents. It's relatively easy to relocate (or even remain in a state while legally "residing" elsewhere). So there are diminishing returns to raising the tax rates significantly on the upper brackets at the state level. I'm not a believer in the trickle down theory but beyond a certain marginal rate many people would just move to a state with a lower rate.

this somehow excludes such human concept as sense of belonging. might be in usa it has atrophied already but sense of home is really important in some places. place where you spend most of your life, where you have you real social network, neighbors and childhood friends. sometimes its lower tax is not worth loosing it all. its not everything about money (for some)

ps im talking about real persons here, not corporations