It's For Your Benefit, citizen.
(Also, the cash advance interest differential for credit-cards, which is higher, and only paid off after all other charges are covered, rather than any sort of temporal ordering)
I take exception to using “citizen”, here, since it implies the gov't is somehow at fault…
In reality, the banks had indeed devised such a scheme, and for the obvious reasons, but it's since been disallowed by government intervention, along with a few other things sucha as actually being able to opt out of overdraft “protection” (this was just a few years ago but fortunately I don't have to care about what US banks do anymore).
FWIW, in Canada credit card issuers are required to apply payments to whichever balances you're paying the highest interest rate on -- it's not even temporally ordered.
UK banks used to have a god racket (don't know if they still do, don't read the relevant blogs) where they'd offer 0% balance transfer cards but with expensive purchase interest. Then, any payments you made went to paying off the oldest debt first (on which you were paying 0% interest) leaving the purchases quickly gaining high interest payments.