Apart from traffic, theft, weather, endurance, weight, obstacles and other issues with the flight, It means an operator will set and monitor each flight. If they manage to increase the endurance, they still have an issue with the costs/benefits equation, especially the cost of the pilots.
A truck can deliver to, say, 4 destinations in an hour, in an area of say 2 miles by 2 miles, and carry far more than 5 pounds with each delivery. Let's say they average 10 pounds per delivery. That's 40 pounds per hour delivered, in 4 sq mi. A drone would not be able to cover as much area - you would need one drone per square mile. So you would need 4 drones and 4 pilots to cover the same area as 1 truck and 1 driver, and only delivering half the weight.