what if the whole region goes down? HA and DR recovery will not work in this case

“If your applications require high disaster recovery capabilities, we recommend that you deploy your instances in different zones of the same region.” - this is from the docs https://www.alibabacloud.com/help/doc-detail/40654.html



i dont understand why this is recommended by Alibaba, what happens if the whole region goes down? in aws they recommend to spread over regions , not only zones. only this will ensure complete disaster recovery.