Other theories, according to Quora, have similar reasoning behind them.
There is a minimum box size to move an item around on rollers. If Amazon wrapped your bottle opener in a phone-sized envelope it could fall down gaps.
Standard-sized boxes are easier to stack and less likely to be crushed under other boxes.
If the warehouse does not have the exact right size box, the item will go in the next-largest container.
According to The Daily Mirror, Amazon promised to stop using boxes quite so large to save cardboard and combat waste. In 2016 it began testing a program to create packages with less empty space in each shipment.
However, it warned that if an item is too “flush” with its box, it risks damaging the item.
In short, Amazon uses too much packaging because larger boxes are easier to handle and less likely to be damaged.