A quick opinion on the square can use.
Using a square can, less space is required compared to a round can. More could be packed into transport planes for destinations not reachable by road.(Common up into the 1960s througout Canada and Alaska). Once more cross continental roads were established like the AlCan the efficiency of space became less as cost of shipping decreased. That's why you tend to see more late squares up there. In the continental US once the interstate system was established trucking overtook rail shipping for faster transport reducing overall cost earlier and round cans became the norm.
Finally can production technology and issues with square metal cans. There are fewer steps to making a round can versus a square can so automation of the process made the round can cheaper to produce. And a round can is more stable and less prone to damage versus cornered cans. When handling larger cans full of liquid it isn't uncommon to ding and dent one. There are no corners on round cans to damage but on a square can a corner could become weak and even pop a seal which could lead to leakage.
With overall cheaper shipping costs coupled with the cheaper/safer round can, it became simple math to eliminate the square larger cans.
That's my opinion on the WHY. You opinion may vary....
