So the big unasked question, and certainly unanswered (unless I missed it): These commercial cloud resource providers provide commercial cloud resources. And us resource users using cloud resources can use commercial cloud resources to supplement our resources to do more work on demand.
But if you're a resource provider, how do you plan for resource provision when you have no idea whether your customers suddenly get a big peak in demand for your resources. With my resource provider hat (not a cloud hat) one of our problems is getting the customers to do planning so we can start buying infrastructure, because there is a long lead time (several months at best) in procurement to deployment.
Perhaps they just massively overprovision their resources but that seems uneconomical. Perhaps they call out to yet other resource providers (but then you need interoperability!). Or they let their customers hit some ceiling, planning for the risk, like the rest of us often do. Just make that ceiling high enough that you hope the customers won't hit it.