I disagree that CYA memos are wasted effort. They serve an important function. They are documentation and internal paper trail devices that give the person's stance on something. If there's an issue that's blowing up around you, it's important to create a document about why you did or did not take action, what authority you had to do it and why you took that action.
In the memo, the original issue is likely to be obscure because in order for it to be clearer, the person taking a stance would have to point a finger at the person they think is at fault. It's better not to do that. It's still a clear and accurate portrayal of what the person is trying to convey. They're trying to convey a CYA memo.
I agree that it has to do with working in an authoritarian organization, but almost all organizations are authoritarian by their nature.