Thing is, many societies are heading for demographic collapse or are already neck-deep in it (Japan). Even if it may be unprofitable now, we (as a society) need to invest serious amounts of money into automating a lot of unskilled labor, because otherwise we will run into disaster.
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.
Someone needs to carry the parcel from the road vehicle, in contrast to a drone that flies up to the customer's window, fire exit or whatever.
Nope ;)
https://www.youtube.com/watch?v=ssrk9bW2xBk
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.
It's clearly the best thing that's ever happened in human history, so far.
I agree that that would be a big disruption, and it would take some time to adapt to a 150% increase in productivity.
Some temporary measures to make the adjustment might be needed.
But it would in the end be one of the best things that ever happened to humanity!