Amazon probably does have some programmatic way of determining how much to fit in a truck, but that’s not what this is. Instead, it’s them trying to cheap out on packaging materials in the dumbest way possible, by figuring out what the reasonably acceptable minimum threshold is for packaging durability but not taking into account size or packing multiples of items at all (as far as I can tell).

This is a pure cost cutting measure on their part. Anything else is just a tangential side benefit.