You're thinking about automation, not drone deliveries.
Where those aspects intersect is that it seems easier to build an autonomous flying vehicle than an autonomous road-going vehicle. Of course, drones have their own downsides for deliveries, including cost because of small payload.
Drones are quite similar, actually: unless they can safely drop into your garden they'll need some sort of secure storage for you to get your parcel from. They are a number of companies working on this: Basically drone lands on top of a locker station and dumps its cargo into it, then you collect your package with a QR code or similar. Even if drones deliver on the roof of residential buildings I think something like that is needed to keep things safe and orderly.
Where those aspects intersect is that it seems easier to build an autonomous flying vehicle than an autonomous road-going vehicle. Of course, drones have their own downsides for deliveries, including cost because of small payload.