Planet Money or something similar did some interviews with people who use payday loan/check cashing places and asked them why they don't just have a normal bank account. Pretty much to a person they said it was because the fees that the payday lender charged were smaller than the banks and more predictable because they (or their brother or uncle or whatever) got charged an overdraft and then a convenience fee for an account below minimum balance and then and then and then and it all turned out to be way worse than just paying for a single financial service. Most of the "unbanked" are just as intelligent and rational as you or I, but for other reasons choose not to get entangled with the banks.