Conspiracy theories develop when official explanations don't jibe with the evidence or when some people think that the two don't fit. In this situation, sensible people look for answers that do make sense. Those, who don't want them looking, call them conspiracy theorist nuts to discredit their search for the truth. Considering an alternate explanation when the official one seems unlikely to be true is seeking the truth.
Cognitive dissonance is being introduced to information that is proven to be true but, if accepted as fact, means that everything you previously based your understanding of the world on, is false. Many, in fact most, will reject the new, proven truth and cling even more tightly to the discredited, old truth. This is probably a natural defense mechanism that is triggered when, as you say, they need to postpone rethinking how they see the world. This is avoiding the truth, not seeking it.
The motives for conspiracy theories and for cognitive dissonance are the opposite.