Earlier quoted context omitted.
It's quite common in cloud solution design to design for failure. One of the common assumptions that we hold to is that one region may go down. Other examples: Assume an instance of an app can go down. Assume a VM can go down. Assume a DC can go down. This is not to excuse the downtime in any way.
Do people ever worry that an entire cloud provider may go down, or is that too unlikely of a case?
Plus the fact that without serious investment, you're probably more liable to decrease availability by going multi-cloud thanks to the increased system complexity.