> I don't believe you can "halt everything" if you go over a certain amount though.
You're pretty much on point. Handling a hard cut is simply not feasible for nearly all services. I.e. simply sending E-Mails in the middle of a news letter is not useful. You can have reasonable actions for some services (i.e. disallow new EC2 machines, add the end-of-month-cost for running ones to the bill), but this could break automation in strange ways (i.e. you suddenly could not spin up a large instance temporarily due to the limit). And how would you handle traffic? Disallow peaks? What about API gateway or other usage-based services?
Lastly, AWS is all about scalability. Breaking so much, especially in the scalability space, for such a small feature is simply not worth it for them. So usually they're simply lenient on bills and take the occasional beating (and it's not like there would not be an equal amount of articles on "how AWS caps broke our system [and it did not warn us/the UI was bad/ ...]").
The missing hard cap is the reason I don't have an account there, but I can absolutely understand why they don't have it.
