This is just about efficiency. Postal (including UPS / FedEx) can plan the route ahead, stack parcels with as little space as possible, and deliver hundreds of packages in a day. UberEats doesn't know when will order show up, doesnt know when will order be ready, it can deliver maybe 2 - 3 orders in a row, the route planning is just in time.

Tell me how is this only explainable by socialized system.