Often SCI documents can reveal how their information was collected, which is much more damaging to our intelligence network than the information itself. The "info" probably is already known by the adversary! Of course, Trump sees our sources as "rats" even though they are working for the US, because they weren't loyal to Putin or whatever adversary of the US they supposedly work for. This is all about Game Theory: Concealing what you know. That's way to complex a subject for somebody like Trump.

It also applies to sigint: How we can eavesdrop through technology is a much bigger secret that the info itself. This goes all the way back to Alan Turing breaking the Nazi enigma codes in WW II. We probably won that war because we could read all the Nazi encoded message traffic, AND we went to some real cost in men and ships to make sure they didn't know that we could.