The article mentions that us-east-1 is the largest region. That's not the only reason why its failure would be so catastrophic. It is the original AWS region and a snowflake among regions. That in itself doesn't have a clear direct consequence--what does is that AWS itself depends on many services specifically in us-east-1. Losing us-east-1 could mean failure of many services outside of us-east-1 as well.

If you were planning a multdatacenter strategy, it should also minimize the number of AWS offerings used or expand it to be multi-cloud.