I voted other. While the Moon Landing Hoax is a part of it, I think it has more to do with the powerful nations which were involved in the Cold War and the Space Race. Their space programs didn't know at first that Earth was flat when they faked their missions. Now they probably do know, but admitting to the series of hoaxes (including but not limited to the Moon Landing) would be a PR disaster. Nations which developed space agencies after the Cold War have probably been secretly threatened by the powerful nations to keep quiet or face the consequences.