[quasse]

It sounds to me like they are in fact running a giant devops system, all for the purpose of not using virtual static IPs.

Instead of just provisioning fresh VMs and migrating customer data they're doing this massive upgrade in place on existing machines to avoid losing the assigned IPs.

I guess they decided the benefits of being cloud provider agnostic outweighed the downside of spending months of man hours automating in-place OS upgrades.

[contingencies]

A good system can handle multiple requirements. You present a false dichotomy.