Interesting, I saved roughly 2M USD / year for customers moving them to the cloud. Your example is silly, all of the CDN I set up has very strict limit on how much a single IP can use and have multiple alerts if you are passing 100, 200, 500, etc. USD limits. On the top of that if that is not enough you can add more limitations to avoid that exact scenario that a public resource can be abused to cause you financial troubles. It won't "bankrupt" you if you do it right. Just like pretty much every other technology, you need to know it.
The other problem with your comment is that you try to make it sound like it was a single dimension decision to use the cloud. It is never a single dimension questions though.
Not taking sides here, but I think that the cloud is complicated enough (especially for a person that does not specialize in it), to miss one of the edge cases that can lead to the huge bill.
In a few minutes, I can set simple PHP script with curl, that will launch 100 requests each second, using a pool of hundreds of thousands of IP's thank to the rotating VPN.
This is an edge case of course, but it can happen.
I use cloud myself, but only cloud servers, which allows me to control budget better and provides me with an "escape plan", where I can just switch to dedicated quickly.
You see this is too complicated and "If you do it right" imply you can get it wrong and go bankrupt. I prefer to use dedicated server with dedicated bandwidth and Kubernetes on top of that. This makes me sleep comfortably at night. I tried the cloud and this was just too much anxiety for me to handle.
It is absolutely not complicated compared to running Kubernetes yourself. You don't have to use serverless and infinite scaling. For things like Azure App Services you don't autoscale to start with and if you want autoscaling it looks like this:
Yes, just like driving, if you doing it wrong you got to the hospital or die, if you doing it the right way you get from A to B. Personal responsibility does not go away because you are using the cloud.
The other problem with your comment is that you try to make it sound like it was a single dimension decision to use the cloud. It is never a single dimension questions though.