Why do economists pay more attention to national economies than to state or provincial economies?

There is a substantial reason why economists pay more attention to the national economies than the state economies. For instance, the national economy provides better indicators on a country's economic health compared to regional whose primary concern is the regions. Moreover, the economic fluctuation in the regions only affects specific areas, while the national economy provides a general overview of the whole economy. Besides, the national economies enable the economist to determine the country's performance on the global perspective, unlike the state economies that rank the economies regionally.