Why so? I'd have thought that in situations like this, one would limit inbound connections, either to certain IPs, or through rate limiting controls, all of which should be controllable at the router / network infrastructure level.

Even more so when dealing with a potential incursion (like servers compromised with botnet software that goes back to work not long after a reboot and slams the server and/or network.)

Some form of demand control is generally how you work around these problems, but maybe those parts are falling over too.

For really big services it's also hard to exercise these processes on anything approaching actual prod scale. Ideally you can chop the architecture into pieces where you can simulate region failure and ensure everything works as planned, and fix whatever you find that breaks with every simulation.

But maybe some bits of the architecture aren't amenable to being regionalized.