Or just have Opsec.

I think there are very few hackers in the world who can hack a national government and not get identified, as the budgets and resources at the state level are enormous, and include ability to seek international help

There is no such thing as "the national government" when it comes to computer systems. They hacked one system of one government division.

If their Opsec wasn't crap it is extremely difficult to try to identify them after the fact.