Here is your answer – and why its an awful idea once you give it some thought. “A round can is easier to produce by curving the sheet around a drum. It stores more volume of liquid per amount of metal used. Aluminum is more expensive than the rectangular cardboard packaging for the flats. Makes way more sense to optimize for aluminum cost to have round cans than to optimize it for “storage”.

Why does food only come in round cans?

Link: https://expeditionportal.com/for

I rant about weird things... a lot. So, canned food is usually in round cans. Square cans would make much better use of precious storage space. I poked around. I found other folks with the same idea. I also found a patent on a canning process for square cans... but I wasn't able to actually...