It's acknowledged by psychologists that the human mind likes order and explanation in order to feel comfortable.
If a massive event happens - moon landing / 911 / death of Elvis / death of Diana, and so on, the mind likes comfortable facts to ensure that everything is as it should be.
The obverse of this is the conspiracy theory - that massive events do not have simple rational explanations - Elvis is alive and working in Tesco, Diana was murdered, 911 was a CIA plot, and of course, the moon landings are a myth.
You can debunk any major conspiracy theory very simply - just work out roughly the number of individuals whose complicity and subsequent silence you would need to make it work, and figure out the odds of any one of them not making the limitless money and fame out of proving any of these events to be untrue - and realise that it is simply not feasible.
All consipracy theories are just that - theories - the product of an inventive and enquiring mind with too much time on its hand.