Why do cereals come in cuboid box?

Answer 1

• It makes it easier to put the boxes into outers for shipment (the outer will also be a cuboid and will have an exact number of cereal packets in it without any wasted space, and the cuboid outer is easier to stack for transportation);
• The cuboid cereal packets stack easier on the shop shelf;
• The cuboid cereal packets stack easier in the cuboid cupboards of [most] houses.

Answer 2

Cuboid boxes can be grouped together to make larger cuboid shapes - without space being wasted between the boxes. This makes bulk transportation more economical.