[nradov]

Banks don't have to allow overdraft. That's an optional lending service.

[jpindar]

But if they don't allow overdrafts, they can't charge overdraft fees.

[jonahbenton]

It is an optional service, one that is highly profitable ($billions per year for each of the large banks), and one also that arguably best serves the customer's interest, as not making a payment in most cases is far worse for many reasons for the user than making the payment and getting charged a service fee.

[keneda7]

And you hit the nail on the head. It all comes back to the dollar in the end. Making the most money per customer.