I have a subjective feeling that Stack Overflow is down a lot more than other websites. I don't see that ever mentioned in the discussion of cloud vs on-prem which makes the discussion seem lacking.
Randomly, packets time out on the internet, I would take this random dashboard with a grain of salt, we cannot be sure SO had a outage just because one request happen to fail.
I have personally seen Stack Overflow be "under maintenance" or straight up down a lot more than I have seen entire us-east-1 down.
Just because you tick a checkbox doesn't mean it'll actually work as planned, and unlike infrastructure within your control that you can actually test (pull the network or power cable from a live server if you need to), you can't simulate a cloud provider outage.
> multi-AZ or even multi-region is much more straightforward than renting another rack somewhere.
Assuming that enough of the AWS control plane is alive to actually allow you to login and administer the services in your backup region.
Furthermore, cloud providers are their own businesses and are constantly in motion (introducing new features, etc). That's good for their business but bad for yours, as it means they might be doing risky changes that could affect you should it go wrong.
We have that because we have complete control end to end. We made an engineering decision not to have geo-redundancy because many of the dependent services aren’t available that way either.
Because of the compute requirements, running that service in AWS or GCP would cost about 80% more, inclusive of all costs (equipment, labor, utilities, etc)