I have been told, by (if I'm remembering my source right) someone who has worked as a UPS driver for 30+ years, that Amazon does that on purpose. Because the variable they're optimizing for is not "are we wasting cardboard". Cardboard is a renewable resource, which also recycles really well, so a little wasted cardboard is not a big deal. What they're optimizing for is packing the truck. Your item arrived in a too-big box, because that box (and the air within it) was calculated to fit exactly into what would otherwise have been empty space in the truck if the box had been smaller. In other words, you know how sometimes inside a carboard box, you'll find the item you ordered plus another smaller (and empty) cardboard box used for filler space? That's exactly what they were doing, with your box as the filler space in the truck so that other boxes wouldn't slide around and damage their contents.
... I see someone else has posted this elsewhere in the comment thread. Eh, I might as well post this anyway, because it's confirmation from a different source.
The other boxes would slide around anyways after your box was delivered tho?
That's a concept that might make sense, and it is something that I've heard from others over the years.
Except: The hypothetical perfectly-packed 53' trailer that leaves the originating warehouse is not the same trailer that delivers stuff to my doorstep. Things get sorted and re-sorted as they move along. It ultimately becomes random instead of optimized, and these random giant boxes take up a lot of space in local delivery vehicles.
Besides, the exceptions can be too exceptional to support any notion of it being deliberate.
It's difficult to describe the biggest box I've ever gotten from Amazon, except to say that it was too big to fit onto the seat of the recliner by the door where I usually put these things. I've received full-size, assembled, 1990s tower PCs in smaller boxes.
Inside of that exceptional box was just 3 ethernet cables, each 1 foot long, that cost me less than $1 each. That whole box could have been a brown paper envelope.