I'll tell you why I cook soups from time to time. Maybe this will shed some light on your grandmother's motivation. However, my family loves my soups. If I had to force them, feed them by force, then I would not cook.
We periodically have a bird on our table (chicken, or half a turkey, or we love half a duck). Their bones make great soups, and quite simply. If not the soup, then I just throw away the bones, which is a bit of a pity.
We eat cabbage almost only in soup. There are many delicious roots that I only know two ways to cook - bake or boil in soup, and the soup is easier.
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