Sure. I mean, you can. I live in San Francisco and as often as not, walk to the grocery store. But it's a pain carrying bags around. Not everyone in the world is going to be ok with that when they are used to just packing a bunch of bags in a car. It's ridiculously unrealistic to think that everyone... including the elderly, etc ... will be happy to just use a train that might be a many block walk on each end.

Yes you can get groceries delivered fairly cheaply, but it will be cheaper with self driving vehicles and robot loading and delivery.