And on top of which, these are definitely noisy nuisances, and as a result people are gonna fuck with them, and it's inevitable that eventually it's gonna hurt someone, which'll cause a huge backlash and expensive lawsuits, etc etc etc.
The only situation i can see these being even potentially viable is in very rural areas, where delivery routes are expensive, people have lots of open land for it to safely reach the ground, and there aren't a lot of nearby neighbors to annoy
Given how the "shop and walk out" process worked, they'll probably outsource it to people paid to throw packages on parachutes over your fence while they make a buzzing noise.
The noise complaints and landing safety issues are definitely a problem, but the cost savings potential and sustainability/safety effects of taking delivery trucks (or your car to the mall) off the road is a huge win.
I can see how noise and landing safety issues delivering to your property can really stall this. However, landing to an approved and managed community mailbox (or rooftop delivery zone in dense areas) might avoid some of those issues.
There's still the issue of birds, which do not like these things in their airspace and, depending on the size, will absolutely either attack drones or be maimed by them. Also, helicopters and small planes often fly quite low. We haven't had a great record with autonomous cars, but sure, let's try autonomous flying drones. What could go wrong?
The big issue with autonomous cars are the other cars that are driven by humans. As well as pedestrians and general rules of the road that need to be applied.
In theory drones have problems that are much easier to solve, because there's just less obstacles to deal with.
The big issues will likely be birds, wind, and rain.