I'm not sure the question is quite right. Google and Amazon don't use "the cloud" in the normal sense of a third-party public offering. They own the infrastruc

I'm not sure the question is quite right. Google and Amazon don't use "the cloud" in the normal sense of a third-party public offering. They own the infrastructure that is also used by other customers as a cloud so in one sense it is private cloud but closer to on-prem than anything else. Many other large businesses run on-prem instead of "the cloud" because the cost savings of a op-ex cloud system start to diminish when you already have your own infrastructure/networks/specialist staff as these large businesses have. Again, this is often a mix of traditional on-prem infrastructure and private clouds that offer some sharing of resources to applications that do not need an entire physical server. Netflix, I think is a mixture of on-prem and public cloud but not sure. So I'm not sure if you are asking "why mainframes instead of distributed e.g. microservices systems" or "why on-prem instead of using the cloud".