Others have pointed out: you need uptime too. So a single data center on the same electric grid or geographic fault zone wouldn’t really cut it. This is one of those times where it sucks to be a small country (geographically).

> so a single data center on the same electrical grid or geographic...

Yes, but your backup DC's can have diesel generators and a few weeks of on-site fuel. It has some quakes - but quake-resistant DC's exist, and SK is big enough to site 3 DC's at the corners of an equilateral triangle with 250km edges. Similar for typhoons. Invading NK armies and nuclear missiles are tougher problems - but having more geography would be of pretty limited use against those.