alt Hacker NewsI'm not saying it's the case here, but sometimes the cloud providers themselves have inter-zone dependencies, or even inter-region dependencies that can cause outages in other zones and regions.
For example, AWS us-east-1 outages have caused global outages on multiple occasions, such as https://www.networkworld.com/article/4168878/aws-hit-by-us-e...
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People who don't work on cloud services are usually very sloppy with their wording which I think is leading to some disconnect here. A "zone" is not really the unit of availability for most things people consider the "cloud" for hyperscalers. A zone is like 1-3 DCs and you are very vulnerable to stuff like localized power events. For that reason most services are not offered at the zonal level and if they are you get big disclaimers saying so and lower 9s of SLA.
Most things are at a regional level which is multiple zones. Your AWS us-east-1 is one such region. A lot of datacenters spread across a decently large physical area have to have an issue for a whole region to start having failures.
For GCP it seems like one power event in a DC led to a thundering herd on the rest of the region which was the actual issue here. (which is a pretty significant problem and isn't supposed to happen)
Worked at a major ISP in the 90s with many critical infra customers. True diversity is a lot harder than many imagine.
In Google Cloud, that's a huge no no and you'll be put on a naughty list facing serious scrutiny during the postmortem review.
Disclaimer: I work for Google Cloud.