@flo You have me thoroughly confused. I don’t know what you are getting at? Why does it matter what measure is used as long as it’s accurate. Potato chips should be done by weight, it makes sense. Liquids can be done by weight or volume.
Some products are just held to tradition. Flour is by weight in the package, even though in America we measure for recipes by cup. Pound cake was a pound of flour, pound of butter, pound of sugar, etc, etc. Then we started using cup measure. Cup cakes. Then the meaning of cupcakes evolved.
Butter is sold by weight, but the sticks are marked for tablespoons and ½ cups.
Possibly, it also depends on the packaging machines and whatever is more logical for the mechanism.
You’re overthinking it. Once there is an industry standard then it makes sense to use that standard to be able to compare products. If all of a sudden a soft drink company decided to sell by weight, it would be harder to compare price per oz. If some companies stuck to that method. Plus, some drinks are denser than others, and the weight would vary inside the same size container.