"Forcing a signature" doesn't work with throw-and-go delivery. In the common best case, someone is home and takes a few minutes to get to the door. In the average case, nobody answers and it needs to be redelivered several days in a row. Making this more efficient would require redesigning last mile delivery to include scheduled time windows, buffering packages per-recipient, etc.

In the early 2000's I was adjacent to a company designing a locking box that delivery services would have the code to and leave packages in. I don't think this went anywhere because it was too far ahead of its time, but I could see Amazon encouraging something like this for customers in problematic areas (weren't/aren't they trying something with being able to open your garage door?).

IME whether you need to return something really depends on the item and why. If it's damaged grocery items from Target/Walmart/Chewy, nobody really wants them back. Whereas Amazon invariably wants the stuff back through their automated solution, but talking to someone (which I only do for exceptional cases) seems to invariably result in "just keep it" and a refund. I'm sure there is some surveillance-based solution behind this, deciding based on social credit score and whatnot. My only questions are how singular it is (eg Retail Equation), and when that dystopian hammer is finally going to drop.