It's the rural-metropolitan divide. Often the poor in rural areas are also Democrats. But all those farmers (huge land wealth), car dealership owners, plumbing empire magnates, or trucking magnates, are incredibly Republican.

But rural areas have far less opportunity than urban areas, and the wealthy often pass their empires down to their children, further hoarding opportunity. So even though there is a ton of wealth for a few at the top, there's extremely little opportunity. Urban metropolitans often offer much more opportunity, as well as greater amenities in the form of culture etc.

Democrats have become a coalition party of the cultural and economic elites as well as the subsidized poor. Republicans tend to be the party of the working class.