You're configuring something that costs money (electricity, hardware, real estate) to provide. Either it's "pay as you go" or you have a flat rate and a cap.
If you have a cap and then your thing hits the front page and suddenly has 10000% more legitimate traffic than usual, and you want the legitimate traffic, they're going to get an error page instead of what you want. If there is no cap, you're going to get a large bill. People hate both of those things and will complain regardless of which one actually happens.
The main thing Google is screwing up here is not giving you the choice between them.
it's not an either or, they can easily let me configure any kind of behavior that I want. No cap, a hard cap, a soft cap, a cap that I program with a python script, a cap where I throttle, a cap where I opt in to deleting certain machines to save money. It can all be done. People are complaining because obvious features are not provided. People would not be complaining if they had all the options that we needed to control how to scale resources in response to load, not just technical load but also financial load.
The main thing Google is screwing up is that if my API key somehow leaks and I end up with extremely out of line billing at Microsoft, I will be on the phone with a customer representative as soon as we or they notice something weird happening and a solution will be found.
Google will probably have me go through five bots and if, by some kind of miracle, I manage to have a human on the phone, they will probably explain to me that I should have read the third paragraph of the fourth page of the self service doc and it's obviously my fault.
Imagine the outrage here, when a company credit card expires and the cloud provider terminates all their instances, deletes all your storage and blob backups?