It was easier to send men to the moon and return them safely than it would have been to fake and not have word of the fraud get out.
In the ensuing ~50 years there would have been massive deathbed revelations from many who would have been in on it.
It was a different time. For example, when ‘the bomb’ was dropped on Hiroshima it was a total surprise to the world. No one talked.
When magazine publishers figured out something was happening in Oak Ridge Tn years ago (because Mountain people weren't subscribing to Scientific American in such high percentages) they were told to keep it to themselves - and they did.
It wasn't like today when anyone will sellout their country for 5 minutes of fame (down from the old fifteen minutes) There were also Germans who came over after the war who worked on the space program... and that was also kept secret.