Bushes, trees, Halloween decorations, spiderwebs, rain, sleet, snow, dogs, cats, raccoons.
Delivery drivers are extremely flexible, they can walk around bushes and other obstacles near your door. They pet or feed dogs that appear near the package. What happens to the drone attacked by the dog (or that slices into the family pet who happens to attack the drone).
If you want a special delivery spot on your roof, then should Amazon be sue'd be everyone who falls off the roof trying to retrieve a package.
If things are mapped out well, and the drone can navigate through the bushes and trees near the door, for Halloween someone puts up a skeleton, or ghosty thing that the drone can get all wrapped up in.
Some snowy day, you are out of Popsicles, but don't want to drive because you can't see the end of the driveway. Make your order and expect the popsicles to show up in 30minutes, well the drone gets lost too, and crashes in the neighbors house. Who collects the bounty? The crashed drone might be wanted by the delivery company, but more likely finders keepers takes over. The neighbor is mad about the chip in the side of his house, so he keeps the popsicles too.
All aircraft have limitations in wind. Too windy and they don't fly. Same with small multicopters. Probably 20-30mph will be a limit. No deliveries on windy days.
I could see distribution center to distribution center the drones could work. Will the payload capacity make it financially viable? Probably not for toothpaste, but maybe high end watches and other smaller high value items