Probably because #2 and (even moreso #3) are difficult to evaluate without a great deal more nuance. There's not much of a use case for #1 except (arguably) national security.

I assume what you mean by #2 & #3 is when people collectively or individually say that an idea is not worth the paper it's printed on. In that case, there's a good lot of things that should, ideally, never see the light of day; except as examples of human folly. The anti-vaccine movement and chemtrail theories are examples of this.

I don't know the details of this case at all, but I suspect it falls under the category of the author trying to communicate one thing, but most people understanding the book in a very different way, and the author not wanting to be mis-read.