AWS does have budget notifications that you can set up with a few clicks. It doesn't come by default because AWS doesn't know what's the right amount for those notifications. I already get enough emails from AWS for every account that I make.

I can actually think of possible/real workloads that would burn 2700 usd out of blue in two days and those customers would not be happy if AWS blocks their account because AWS thinks they did something wrong.

AWS Support quite often happily refunds these amounts and you don't need to post to Twitter. I've seen them refund a lot more.

Why haven't they done something to prevent this mistakes? They already refund these things, it's just those refunds is a drop in bucket compared to services that enterprise customers are paying for, and AWS engineers are busy building for them.

AWS gives you a lot of power compared to what you can do on your average hosting provider, but sadly there's also a lot of room to shoot yourself in the foot if you don't know what you are doing.