Yeah, and half the time, the cardboard sides of the can would crushcollap, requiring a simple triangular "church key" can opener to open it. With a small vent hole on the other side. Then, it was funnel-time, or if you were a good shot, "aim and drain", always good for a cleanup. But then you could take the towel with that oil on it and go over the big round air cleaner, the top of the radiator, the batery, get all the dust off the horizontals. Clean as new, eh?
What Johnny mentioned, regardless of the actual cost of plastic vs. round cardboard, the rectangular shape of the new plastic bottles saved a LOT of space aboard boats, trains and trucks shipping and storing the stuff. Probably made the merchants that put it on the shelf happy, too.