Not sure where you got “random format” from the comments, but we (U.S.) also use a very precise method for defining the size of paper, which is 8.5x11 and legal as 8.5x14. For the US, both are sized to fit in the same standard envelopes. I’ve never thought, “boy, I really need half this sheet length-wise but made shorter to keep the same aspect ratio for this situation”, so while I can understand why that could make sense when creating an international standard, it isn’t more or less random or more/less precise than any other basis. Our basis simply evolved naturally from our system of measurement and our needs with countries we traded most closely, rather than as an international standard based on a different system of measurement that needed to be shared among numerous countries situated closely together.