[toyg]

And it's why, when paying like that, you're typically paying more than would have done in cash, or the amount is high enough to cover the extra transaction fees. That's definitely the case for most UK carpark operators - the minimum amounts you can specify online are always higher than the ones for cash, because of transaction fees.

You're probably also misjudging how tiny those amounts are. Vending machines, for example, nowadays don't really stock anything costing less than £0.50, if they take credit cards. Public toilets can often be £1 or £2.