Banks absolutely make money on retail deposits, and you definitely are doing them a favor by putting your money in.
Banks do spend a lot on marketing to acquire a given customer, and will then upsell that customer on more profitable products like loans and credit cards. But having a high customer acquisition cost and then upselling is not quite the same as being a "loss leader" (which sort of implies that marginal profit is negative, which is definitely not true).
Banks do spend a lot on marketing to acquire a given customer, and will then upsell that customer on more profitable products like loans and credit cards. But having a high customer acquisition cost and then upselling is not quite the same as being a "loss leader" (which sort of implies that marginal profit is negative, which is definitely not true).