The short version is it seems like a big "gotcha" that there is no way to limit bandwidth or spending on that or other resources ahead of time, and that might be a deliberate business model that is more aimed at well-funded startups or large companies that are monitoring costs much less closely than an individual or small business.
It's not necessarily too hard to just not dynamically spawn a bunch of machines, but the bandwidth one is going to sneak up on people.
Lots of people want limits. They might make sense for something like Sprites, where the end-users are often (but not always) individual developers. They're terrible for hosting fixed-function applications. The real gotcha is having limits, because that's the host effectively taking your app down for you.
I know talk is cheap, but I've been in the room for every one of these discussions over the last 6 years at Fly.io, and if we could have come up with a system to make limits workable, we would have done it. Charging for stuff you don't want is bad business, and we make our money from happy, growing customers (the open secret of hosting is that a huge chunk of usage is basically a loss leader search for a much smaller number of ultra-profitable customers).
These pricing models --- at least outside of AWS (I'm not cynical about them but their incentives are different from indies) --- are not meant to fuck you.