Firstly, let me just say, technologically drone delivery could definitely happen. There's no technical reason why not.
But if we look at the history of freight it has always been about efficiency, and new competitors have always competed by finding ways of being cheaper.
We already have less technical "drone delivery," it is called a courier, but outside of New York and a handful of other places they're niche. Nobody wants to pay to deliver just a single package, it is too expensive.
Even services like "next day delivery" work on the principle of economy. You have trucks which are on other deliveries (economical ones) just drop off the "next day" packages between them. That makes these "unnaturally cheap."
What do drones offer that a human courier doesn't? It cannot deliver inside most office buildings, you're still paying for fuel/maintenance/development/lost drones/etc. It likely has limited capacity.
Plus let's look at competing technology coming up: Automated vehicles. How long until a delivery van can drive itself to your home, and then send you a text to meet it outside? That technology is coming with or without drone development, and solves some of a drone's inherent issues (poor capacity, lower maintenance, better economy, etc).
I really think drones for deliveries won't go anywhere. It is just a fad thing because companies want to be cool. Too many problems/limitations/high costs, and few benefits. And as I said automated vehicles will kill any remaining shot drones may have had.