I assume they sell candy for the same reason art supply stores sell candy -- it's easy to sell, because people like it.

The combination of products is basically "everything you might find at a 'supermarket' in another country, except for the food", and I assume it's that way because grocery stores are primarily dedicated to food. If you took the food out of a Carrefour, what would it be selling?

(We also have stores on the "full supermarket" model, Walmart and Target.)