Hoax theories exist and grow because people quite like to think that the 'powers-that-be' are deceiving them.
A gentle non-threatening feeling of paranoia is appealing to a large number of people - most of whom have too much time on their hands - and thus, conspiracy theories abound.
Psychologically, we feel more comfortable with momentous events if we can debate their veracity, which is why the majority of long-running CT's are about such hige events as moon landings / 911 / death of Diana, and so on. People find it hard to accept that these things did actually just happen, so we ponder the alternative that we are being duped. It's built into out psyche, and exploited by CT debaters around the world.
You need think no further than this - given the massive number of people (hundreds of thousands) involved in the massive logistics of a space programme, and the likelhood that every single last one of them would refuse the fame and millions that would arise from debunking such an event - and you can see that there is simply no possibility that the moon landings were faked.
OK, my work here is done ...