Only one item can be delivered at a time. It can’t weigh more than 5 pounds. It can’t be too big. It can’t be something breakable, since the drone drops it from 12 feet. The drones can’t fly when it is too hot or too windy or too rainy.
You need to be home to put out the landing target and to make sure that a porch pirate doesn’t make off with your item or that it doesn’t roll into the street (which happened once to Lord and Silverman). But your car can’t be in the driveway. Letting the drone land in the backyard would avoid some of these problems, but not if there are trees.
Amazon has also warned customers that drone delivery is unavailable during periods of high demand for drone delivery.
Aerial drones are a particularly stupid method of delivery. Delivery trucks, combined with terrestrial delivery robots are a much more versatile approach.
Delivery trucks require a human to drive. And despite the insistence otherwise, we are a long long way from any sort of automated driving system. They also operate on a 2-dimensional plane and have to navigate around a variety of structures.
Conversely, aerial automation is significantly easier since it is 3-dimensional and there are not obstacles to navigate. This also means it’s much easier to automate.
Companies like Zipline have been operating these services for many years now with great success.