It seems more likely that they exist for the same reason the numerous shops selling various small cheap items (phone box shaped fridge magnets, hats with "I lov

It seems more likely that they exist for the same reason the numerous shops selling various small cheap items (phone box shaped fridge magnets, hats with "I love London", etc) exist. It's a way to fill a commercial unit until a more permanent tenant arrives. So they shut down and reopen elsewhere because the situation was always temporary.