Much as with backups - if you don't test them, they don't exist.
Everywhere I've worked has had multi-AZ infrastructure. I have never worked anywhere where the failure of an AZ has been simulated regularly, with second-order effects mapped out.
It's like our on-prem systems were ordered to plan out and exercise DR plans to account for a data center going offline, but we can't exercise a DR plan fully if part of the plan is 'Adapt to how application X, which is hosted in the same datacenter, also chose to fail over.' We do not own application X. There is no appetite in the business to co-ordinate the DR exercise across the entire company at the same time.
We can't even do it all in a lower environment because there are dependencies on systems that are shared across environments. Some massive, redundant filesystem that is sync'd across our data centers, but the sync is a boolean. One datacenter instance of it is the primary and the others are read-only until they get promoted. We have one of these and lower environments are just a different root folder on the system with different access patterns, but they can't make DataCenter A the primary in prod and DataCenter B the primary in UAT.
Since most companies would have to do it in production and they don't want to have customer impacting outage, they tend to do it during an actual outage.
It seems like a lot of work, and it seems that as architectures evolve it would be hard to ensure that the multi-AZ failover works well.