If most startups implement this solution wouldn't the problem just replicate itself to regions instead of availability zones? I think the problem would be less

If most startups implement this solution wouldn't the problem just replicate itself to regions instead of availability zones? I think the problem would be less severe across regions than across availability zones within a region and here's why. A major benefit of multiple availability zones is the low-latency connection between them. That encourages you to copy instances, EBS volumes, S3 buckets, and RDS data between them, most of the time en masse in the event of a failure. Across regions, you're sending data over a slower connection, so you have to take care of replication on an ongoing basis. So your instances, EBS volumes, S3 backups and RDS instances and replicas would already be in the secondary region when failure occurs in the primary. I'd compare it to having a vacation home and spare car in another state when an earthquake hits, instead of looking for a shelter near the disaster area.