They say that the Moon landing was shot on a sound stage, however, have you been to a movie set? There are a lot of folks there that would have had to keep quiet.
I'm pretty sure that the way the hoax theory gained momentum is that there were certainly people who doubted we did such a thing and then that
Capricorn One came out in the 1978 (they are making Capricorn Two BTW) that shows NASA faking a Mars landing and it all goes wrong. Obviously the movie maker got the idea from the hoax theories and took it a step further which generated more interest in the theory in the late 70's
That was also made at a time when you couldn't shake a stick without hitting a show like "In Search Of" or a show on Erich Von Daniken, the Bermuda Triangle, Kirlian photography, Uri Geller not to mention a multitude of movies like The Excorcist, Close Encounters, The Omen, Amityville, etc. People eat that shit up. I did, at least for a while and it lets imaginations run wild. It's easy to get fact and fiction mixed up.