It is the human tendency to deny the reality of "conspiracy", even though all of human interaction is by definition a "conspiracy". Conspirators rely on this habit of denial, because it makes their conspiracies possible. As long as people are denying that conspiring is possible, then conspiring is guaranteed to be successful.
"Nobody would do that. Nobody would even think of doing that."
The credo of the most successful conspirators is this: "Make what you do so far removed from normal thinking that normal thinkers would never even consider it possible."