Truffles are not farmed much because the point of truffles is to be a rare and expensive food.
No one would buy “farm-raised truffles” because that product wouldn’t supply them with what they buy truffles for in the first place: the feeling of being a fancier person than their neighbor. It’s the same reason why caviar is expensive despite delicious fish roe being extremely common in nature (ask a fisherman sometime how frequently they catch a fish that happens to be full of eggs).
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