Trader Joe’s buys directly from suppliers whenever possible, bargains hard to get the best price, and then passes the savings on to the consumer.
If an item doesn’t pull its weight in their stores, it goes away to gangway for something else.
They buy in volume and contract early to get the best prices. Most grocers charge their suppliers fees for putting an item on the shelf. This results in higher prices… so Trader Joe’s doesn’t do it.
They keep their costs low—because every penny they save is a penny you save.