Different states have different levels of economic development. Since all states share a common currency, it isn't possible for states like Mississippi to devalue their currency in order to be competitive with California. Large fiscal transfers between states are necessary to keep things balanced out.
Why don't they just sale their goods at lower prices? No need to fiddle with artificial (non-gold-backed) currencies.
The US political system gives disproportionate influence to people living in less populous states.
This would only be the determining factor if you believe that California on its own would not vote for the federal government providing support for the lowest income people.
The evidence seems to indicate that is not the case.
They wouldn't as much as they are forced to now, especially if they were an independent country (which is the only fair comparison).
There's also efficiencies of density that you just don't get in Mississippi, but that also pays off as a redistribution within states from cities to the suburbs and countryside.
A few reasons. Less populous states have proportionally more representation, since representatives are proportional to state population but every state gets two senators. Rural states are earlier in the presidential primary season (Iowa is the first), so they wind up getting more. And the less populous states tend to be poorer in general, so they have less to give and greater welfare need.