US post-war neighborhoods built after the advent of cars, were mostly designed for them. It's not madness, as much as it is the inevitable result of consumer demands for what was at the time, new housing.
> Does this not represent a huge opportunity for someone to start a local grocery store business?
Those stores do mostly exist where they are viable. The limiting factors are:
1. many of those neighborhoods don't have commercial space, and are filled with people who live there specifically because they do not want to live by commercial property, and support zoning regulations to keep grocery stores from being built besides their property.
2. because many people do have cars, neighborhood grocery stores are sometimes at a commercial disadvantage, because many of their potential customers can easily drive to stores with greater selection.
I do like living in more lively neighborhoods, and I picked one where I do have two small grocery stores within 15 minutes walking distance. The thing is, they're both ethnic grocery stores with limited selections. I try to support them when I can but to get everything that I want to buy in one shopping trip, it's much quicker and easier to drive out of my neighborhood to a much larger store.