Others have mentioned the parking lot sizes. If we wanted the best of both worlds, we could have online shopping at Costco with curbside delivery. There has to be a warehouse somewhere which means there are trucks/trains/planes moving goods around regardless. Even Amazon builds warehouses closer to where things need to end up eventually to optimize costs. You are comparing apples to oranges.
Finally, Costco delivers if you really don't want to leave your house. Now we are back to the same model but with far more flexibility.