Why aren't there more walkable grocery stores especially in South Philly?

Living in East Passyunk and the only walkable options are South Philly co-op, corner stores or wading through a giant parking lot to get to a terrible ACME. For the density and wealth comparable to neighborhoods in London there would be like 5 Tesco's (comparable to heirloom markets) just on the avenue. Just turn that dumb city parking lot near Morris into a trader Joe's and offer no parking since the density per square mile is like 60k in that area.