It's mostly a zoning problem— for whatever reason, America treasures areas of purely single-family homes, probably because it creates an economic barrier that enforces a general demographic sameness in an area. That means that, even if you wanted to open a corner store in a neighborhood by building a storefront at the base of a house, as was traditional in the United States (e.g. http://www.moline.il.us/images/pages/N716/1403%207th%20Ave%2... ) it'd be illegal.
And Trader Joe's can and does operate in no-parking storefronts in sufficiently dense neighborhoods.
And Trader Joe's can and does operate in no-parking storefronts in sufficiently dense neighborhoods.