Most of the US is rural with no housing, therefore no affordable housing by definition. In most small towns you're even more car-dependent than in a city, and there are no jobs.

As I think about it, if we define affordable as "costing under $500/mo all-in" (since that would be a little over a third of one month's work at minimum wage), it would surprise me if even 1 in 20 homes met that criteria.