They don't make money on the interest on the minimum balance, they make money on the total balance. True, for some customers this will be very low or zero. But

They don't make money on the interest on the minimum balance, they make money on the total balance. True, for some customers this will be very low or zero. But as long as some of the companies they work with have money in their accounts (not an unlikely state of affairs), they can make their money from those accounts. As long as they've set up their underlying tech stack such that the marginal cost of an extra account is nearly zero, then offering accounts with no fees or minimum balances is useful way of attracting customers, many of whom will grow into good sources of revenue.