Cups are only practical for small amounts anyway, such as 2 cups or 1/2 cup. A commercial sized recipe calling for 10lb or flour or 2lb of chopped onions would

Cups are only practical for small amounts anyway, such as 2 cups or 1/2 cup. A commercial sized recipe calling for 10lb or flour or 2lb of chopped onions would be highly inconvenient to measure by cups, even if you did have the necessary set of cups in big sizes (10 cups, 50 cups, etc). Much easier to measure large amounts by weight.