Why is milk sold in rectangular containers, while soft drinks are sold in round ones?

After reading the answers in the book, this is my summary and understanding..

- Milk containers are rectangular in cross-section so you can pack them closely with lesser unused space, unlike round containers.

- Milk containers need to be stored in refrigerators (hence the need to be packed closely as space is a premium in the refrigerators), while soft-drinks can be stored in open shelf.

- Soft drink cans are in round containers because it is easier to hold in the hand when drinking direct. One seldom drinks milk directly from the container.

- Cylindrical shaped containers are better able to withstand the pressure built-up from carbonated drinks.