It's the slow and steady increase in prices that made it so profitable. About 5x over inflation during Buffett ownership.
This has happened to far too many items over the last few decades. Most of the things drugstores sell are cheap to make, but have steadily increased in price in the US over the last few decades. Vitamins used to be priced according to manufacturing cost. Slowly, the low-cost vitamins have been up-priced to match the expensive ones. Vitamin C is about $10/Kg in bulk, but about $100/Kg at a US drugstore.
This has happened to far too many items over the last few decades. Most of the things drugstores sell are cheap to make, but have steadily increased in price in the US over the last few decades. Vitamins used to be priced according to manufacturing cost. Slowly, the low-cost vitamins have been up-priced to match the expensive ones. Vitamin C is about $10/Kg in bulk, but about $100/Kg at a US drugstore.