Funnily enough floods (GCP) and fires (OVH) are two of the 3 things AWS explicitly mentions in the Well Architected docs. For a lot of companies an AZ going down is an annoyance or bad day but a whole region going down could be a real continuity risk.

> Each Availability Zone is separated by a meaningful physical distance from other zones to avoid correlated failure scenarios due to environmental hazards like fires, floods, and tornadoes.

https://docs.aws.amazon.com/wellarchitected/latest/reliabili...

Unless they’re in us-east-1 and it’s an Amazon software/service fault.

And different flood planes. Source: I was at AWS 2008-2014.

It makes it very easy for me (as someone who comes from a world of physical datacentres) to reason about what an AZ is getting me, and also to understand the benefits of using AWS (not having to think about the details of power routing, blade switch vs top-of-rack vs core switch, storage cabling, blah blah blah).

If I have to think too hard and do too much work about how I lay applications out, I might as well just rent in a colo.

It’s more than that. AZ’s are geographically distinct as well along multiple dimensions include flood plains etc.