What you're trying to get at is this: would you rather trust your infrastructure to a large organization whose core competency it is to do so, or would you rather manage it yourself? For many companies it makes more sense to have someone else manage it because of division of labor.

If you believe you're better suited to managing your own hardware for cost or capability reasons, you should. But of the arguments in favor of that decision, pointing out that "you cannot do anything" when GCP/AWS/Azure has downtime is a pretty poor one. It's an exceptional circumstance if you're 1) able to achieve better uptime than a cloud provider, 2) at nearly the same cost (in personnel, hardware and software), and 3) while being relatively unaffected by the downtime of major cloud providers anyway.

The companies for which the calculus shifts in favor of managing their own hardware probably don't need to be told "the cloud is just someone else's computer." In contrast, most companies using a cloud provider do not have a readily available alternative because they do not have in-house talent capable of maintaining baremetal hardware (local or colocated).

I consider myself personally capable of maintaining a baremetal distributed system with high availability, because I presently do that. But for the most part I wouldn't encourage companies using a cloud provider to invest in their own infrastructure. It's usually expensive in personnel, time or both.