In the mildest defense of Rowling she actually did put it into the books that you can't just poof food into existence. Summoned food has no nutritional value and duplicated food has its nutrients halved, the food was cooked by house elves and teleportex to the dining hall. It's explained somewhat similar to how folks can starve on lean meats, you are physically full but without something in addition you'll just starve to death, it's actually an element of the last book that the main cast are slowly starving to death for a bit.

Though none of that stops them from producing food via other magical means such as what amounts to magical automata. Pretty sure the car in book two had animalistic sentience by the point of the spider subplot, so there's nothing stopping them from making magic farming tools that do that all automatically. They really should be a post scarcity society, but well Rowlings a shit world builder.