I'm not defending anyone here, just adding in the bits I know that "might" help to explain it.
The "Pay at Pump" service was off at that station for a time last week, this could suggest that they did have a terminal fault. It could also be that they wanted as many cards brought inside as possible, but unlikely as you're just drawing attention to it.
The newer cash terminals do have the ability to "limit" cash amounts when they are getting low. You can normally draw £250 a time out of this, four withdrawals and that's a thousand pounds out, so it needs a LOT of money inside it, to which the normal staff don't have access to. When the machines are filled you tell it how much you have put in, when it gets low it notifies that a refill is required and limits withdrawals. This does mean that you can't draw out a lot of money, which could be a minor inconvenience, but it stops the machine being emptied as quickly, which could leave people without money to pay for their fuel etc.