> So much for the folks defending these three companies that refused to provide hard spending cap ("but you can set the budget", "you are doing it wrong if you worry about billing", "hard cap it's technically impossible" etc.)

Yes, it's technically+business impossible. To implement a hard cap, a bill never to go over, they'd have to cut your service, but also delete all your data in databases, object storage, data lake, etc. This is simply not an option, so they take the different option of authorising support to wave surprise surcharges / billing DDoSes.