Earlier quoted context omitted.
You speaking of rational responses. You likely refer to the rational expectations hypothesis in economics. The default assumption is of course that everyone makes rational decisions, including the poor. Since they are making decisions that you don't think are rational ("it's probably rare for the optimal solution ..."), you conclude that the reason is that the poor people are less well-informed. This makes sense, so…
It's not the rational response at all. The rational response is to get a bank account like your wallet. One that ASKS YOU explicitly for permission before paying out money to someone else. A bank account is not that, at all. A credit card is closer to that (because of chargebacks). Prepaid credit cards, and getting a new one every month (carrying over the balance, and because of the number changes, it's very hard to…
You propose what you think should be a better solution. This history so far shows that your solution is not clearly better. Just this month "The Consumer Financial Protection Bureau issued a bulletin warning employers against using only so-called payroll cards to pay workers." ... "Complaints received included fees for withdrawing cash and checking card balances. Critics say payroll cards with high fees mean that some workers are essentially making less than minimum wage." -- http://www.usatoday.com/story/money/business/2013/09/13/agen...
Yes, there can be a time where that's a better solution than a check.
However, we are not yet at that time, so it's not a rational choice NOW.