1. Even if you assume perfectly good intentions, they're not incentivized to fix the problem because they're not on the hook for the bill, but stand to profit from it. Their margins are eye-watering, so sending out a $100k bill for a service which cost them no more than $5 to provide doesn't have a downside (other than bad PR, which they seem to be blind to).
If providing this bandwidth cost them $50k rather than $5, I would bet you my entire life savings that they would QUICKLY find a way to add hard limits to their service, no matter what technical challenges they're quoting now.
2. This is probably a 95/5 problem. The vast majority of these sorts of cases that I've seen and read about are caused by increased traffic, which hits the customer either with extortionate egress fees or unintended compute scaling behavior (FaaS/VMs).
Storage is trickier, but you could stop accepting writes or reads after passing some hard limit.
This leaves some edge cases, sure, but it should handle the vast majority of unexpected bills without any destructive actions.
> You can set an alarm in AWS today and the user can decide what to shut off.
That shifts responsibility back on the customer, which is exactly the problem to begin with. I need assurances that I won't be billed more than $X in any given day, or month and this solution doesn't provide that. Maybe their API down, maybe it's serving stale data, or maybe my automation fails for some reason.
> How is all of this communicated?
Hard monthly limits:
Egress: [ $ 10 ] - When exceeded, all outbound traffic is limited to [ 0 Mbps ].
Compute: [ $ 10 ] - When exceeded, scale all compute instances to [ 0 ]
Data Storage: [ 1 TB ] - When exceeded, all writes are rejected
Reads Ops: [ $ 1 ] - When exceeded, all reads ops are rejected
It's really not that hard. Offer these limits on a per-project, or even per-resource level, that would naturally allow you to limit the blast radius. A personal website that has gone viral would likely want to have different limits than an email server under the same account, for example.