[Cthulhu_]

Twenty odd years ago, we had a system like that though, despite there being multiple grocery stores in walking distance. Some people have mobility issues meaning they can't walk / cycle to the shop, but a grocery store on wheels is fine. It was called the SRV Wagen, which stood for "sell rationally together" when the scheme was started in the 70's. There are still 100 of these vans active last year apparently.

Anyway, think of it differently, instead of a need, why not a want? It's not that different from having groceries delivered to your home. Maybe not as scalable, but it's a valid buisiness model, especially in rural areas.

Nowadays I think it's becoming more of a need again; with the migration of people out of the small towns, more and more grocery stores have decided to pack it up because they just don't get enough customers anymore. A mobile shop that frequents multiple towns every week is a valid replacements.

And as another commenter mentioned, it's not limited to just groceries; we also had a fishmonger, and everyone remembers the ice cream truck. I don't see why hipster food trucks don't actually truck around either.

A more recent example, an ice cream truck would park out front of office buildings and ring its bell. A tiny coffee trike would park in the train station in the morning, then do the rounds at the office buildings nearby throughout the day. The important thing with those services is that they consistently appear on the same day and roughly hour, and that they have some kind of audio cue.