Even if you could keep the bread fresh, I doubt you could sell it at a profit in Chicago or NYC, after sending empty trucks on a round trip to Mexico, and back, even if you were given the bread at no cost.
The larger radius in sparsely populated areas isn't due only to a more spread-out distribution base, it is also due to the fact that much lighter traffic allows for far better distance coverage in the same amount of work day.
I know this from a previous job which included distribution of bakery products. In very densely populated areas, your distribution radius is even smaller, sometimes as little as 15 or 20 miles.