Not surprisingly, there's more to the story.
There's one theory floating around the internet that claims Amazon is playing Tetris with its packages:
This makes no sense. When packing a truck, the idea is to fill the cube as densely as possible. Pack more widgets on a truck and the cost to ship each widget goes down and it looks like others agree. No one would purposely leave space in a trailer to protect packages. That's what air pillows, bubble wrap, Kraft paper and other kinds of protective packaging is for.
Reddit user, itsachikenwingthing, says:
"Dude I've worked in warehouse unloading Amazon trailers and that is a load of baloney. If only I had a dollar for every time a mountain of packages almost fell on me opening the trailer doors."
While another Reddit user, SaebraK who claims to have worked in Amazon's Phoenix DC, says:
"I was a packer while there... The packing slip has the items and would have a letter code, A1 BO, K, AB, etc. These are the box sizes. You are told from day one to follow that code."
According to an article in technologyreview.com, humans work in close collaboration with computer automation.
Products flow through Amazon's warehouses at a dizzying pace. Orders are picked and sorted in to batches headed for a single customer. The computer knows the dimensions each product and will automatically allocate the right box. It even knows the right amount of packing tape.
But, if the dimensions in the computer is incorrect, mistakes happen. Reddit user westward_man explained:
"Box size is determined by dimensions of the item, not how it’s going to be packed in the truck. When you get a giant box for a small item, it’s usually because someone [messed] up when they measured the item, e.g., they measured a pack of six instead of the individual item. Source: I write software that handles measurements at Amazon."
This seems to be the most logical explanation. The computer specifies a box, it's incorrect, the packer knows it's incorrect but doesn't have the time or the ability to make a change.
Said Reddit user SaebraK:
"So, seeing some seriously stupid box sizes come through, I would down size the box to make sense. The first time I got a passing "Hey SaebraK, make sure you use the box size on the invoice." The next time I got a real warning and told if it happened again I'd be written up."