AZs are supposed to be distinct datacenters within a single region. If all of your customers are in (e.g.) APAC, it's not unreasonable to put all your online processing within APAC, with high bandwidth connectivity between them and from each to customers. You might not be able to do master-master over extremely long distances for performance reasons under normal conditions, but you'd keep warm or cold backups totally out of the area. There are a lot of factors which go into the decision, but there are definitely times when 2 datacenters (often run by separate providers) with independent connectivity, but both within a specific distance, makes more sense than extreme separation.
It's sad how people knew how to do this stuff ~2002-2006 and then forgot it all (or just stopped caring) once the delicious cake of cloud appeared.
You missed my point: this is not a cloud problem except to vendors looking to sell non-cloud hosting. Any region is vulnerable - some clown with a backhoe, congestion / DDoS, routing screwups, etc. have taken out data centers in entire areas (Los Angeles, SF, NY, etc.) even when providers thought they had more redundancy. If you really need it, you spend the money on wide geographic separation.
It's sad how people knew how to do this stuff ~2002-2006 and then forgot it all (or just stopped caring) once the delicious cake of cloud appeared.