Why would it be hard to calculate cost? Multiply a fixed price * requests/time ? It doesn't have to be exact in real time, it just has to report something approximately useful in realtime.
It's absolutely not fine to be at the mercy of other people, that's what we buy cloud products or really any products for: So that we are not at the mercy of hardware faults, bad weather, bad teeth, hunger, thirst, [insert anything]
I'm guessing the answer is simply money. It's less expensive to deal with people like this this than it probably was to prevent it. Right now, they seem to run very sparsely, so ramp that up (if it's every 3 hours and they want to change to 5 minutes that's like a 6000% increase) and they're probably paying more than it costs to employ people to return credits or fears of people leaving.
It sucks, but that's unfortunately the world we live in until something changes.
The US could rely on an agency like the CFPB to prevent this, but that was gutted under the current admin.