See the sibling comment thread. It's just not that simple. It creates a lot of liability, could lead to permanent data loss, and doesn't really prevent any mistakes either (just swaps them for mistakes in budget caps).

AWS would rather lose some billings than deal with the fallout of losing data or critical service for customers (and in turn their customers).

it depends on the use case. For example, I would like to have developer accounts with a fixed budget that developers can use to experiment with AWS services, but there isn't a great way to enforce that budget in AWS. In this case I don't really care about data loss, since it's all ephemeral testing infrastructure.

In theory I could build something using budget alarms, apis, and iam permissions to make sure everything gets shut down if a developer exceeds their budget, but if I made a mistake it could end up being very expensive. Not that I don't trust developers at my company to use such an account responsibly, but it is very easy to accidentally spend a lot of many on AWS, especially if you aren't an expert in it.

So now we have another potential mistake - you setup a "delete everything/hard budget" for a production account instead of a developer account. What then?

It's impossible for AWS to know how to handle hard caps because there are too many ways to alter what's running and it's too contextual to your business at that moment. That's why they give you tools and calculators and pricing tables so that it's your responsibility (or a potential startup opportunity).

Money is easy to deal with. Alarms work. Bills can be negotiated. But you can't get back lost data, lost service, or lost customers.