I would have said it's a case where the zoning system breaks. You get "grim expanses of McMansions" because some city planner ruled by decree that this area ove

I would have said it's a case where the zoning system breaks. You get "grim expanses of McMansions" because some city planner ruled by decree that this area over here is "residential" and can't have little corner bodegas mixed in, while that area over there is "commercial" and can't include housing. In those few parts of the US that don't have zoning laws, you get lots of mixed use. Heck even if a neighborhood was originally all just houses when it was first built, unless some bureaucracy is actively preventing it some people will want to work out of their home and provide services for their neighbors.