But not security. And for governmental data security is a far more important consideration.

not losing data and keeping untrusted parties out of your data is a hard problem, that "cloud" aka "stored somewhere that is accessible by agents of a foreign nation" does not solve.

It's the government of South Korea, which has a nearly 2 trillion dollar GDP. Surely they could have built a few more data centers connected with their own fiber if they were that paranoid about it.

As OP says, cloud is not the only solution, just the easiest. They should probably have had a second backup in a different building. It would probably require a bit more involvement, but def doable.