> Look at e.g. General Mills, based in a blue state, but a great deal of what they buy are ag inputs from red states.

Are the businesses from who they buy ag inputs in the red states not compensated at market rates for the raw materials they provide?

Do the red states also not receive massive taxpayer funded farm subsidies for the corn and wheat they grow from the federal government?

Minnesota's GDP is higher because it has a larger population and a more diverse and greater value-added economy than it's its ag focused neighbors.

It's GDP per capita is actually lower than its very sparsely populated neighbor, North Dakota, but the economic power of a jurisdiction ultimately comes from its population*productivity.