no way will they go back to coin-operated. That would mean they have to pay employees to walk up and down to collect coins.
because I doubt anyone who spends cash regularly is holding much of it long enough to lose value to the digital ones in their checking account.
If you need $6 to pay for parking, and the largest commonly available coin is a quarter, that means you need 24 coins to pay. If the value of currency was such that the parking only costed $3, or if dollar coins were more common, you'd need less coins to pay.
It doesn't surprise me that they want to make hardware maintenance your problem.