You might be overreacting. This is free stuff for whoever picks it up - yes Amazon shouldn't be littering, yes it might inconvenience something but it isn't that bad.
But Amazon isn't going to just abandon the people who bought stuff. They're going to get a different item. This is just Amazon signalling that it is cheaper to deliver a new item than to collect a lost item.
Remember, these parcels aren't being sent through the postal system (where you legally release ownership of mail to the Postmaster General by sticking something in a mail slot, which is how it can be a federal offense to tamper with their mail—undelivered mail is the government's legal property!)
Instead, these are parcels going through Amazon's own logistics carriers. Amazon never released ownership of these items—they don't do that until the item hits the recipient's door. These items are legally Amazon warehouse stock, that happen to have shipping labels printed on them.