Another factor could be weather conditions. Heavy rain/snow/wind could all affect range or even accuracy (heavy precip can interfere with GPS to some degree). Drones also probably work better in a suburban environ, but less in a dense urban area or less dense rural area. Also, maps can be terribly slow to update. My home is in a Chicago suburb, about 8 years old now. Google maps still cannot accurately plot my address. Personally, I dont look forward to "we dropped off your package where we think your address is" and yet the package is a few hundred yards away. I'm also reminded of one of my favorite fuckups, this by USPS: my Mom misquote "street" instead of "drive" on my address, street number, name, city, state and zip otherwise being correct, and the overnight package landed in Florida instead of Illinois...

You forgot the most important thing - noise.

Drones are loud. Incredibly loud.

Probably. I don't necessarily believe it's around the corner or ever will be feasible. But the motivation is clear.