Retail is inefficient. To make a retail purchase, you have to drive to the store and back, while a delivery driver can pick an optimal route and make multiple local deliveries with their vehicle before returning to the warehouse.

To give a more concrete example, to purchase a souvenir, some personal hygiene products, some computer hardware and some spices, I'd have to make 4 stops, spend at least 2 hours and $6-8 worth of gas.

None of these things are day2day critical, like food, or essential to physically inspect before purchase (like home improvement goods)