Hollow Moon Theory. We went to the moon, something horrific happened, and now we absolutely refuse to go back. NASA would repeat the first reason as justification, but the actual true reason is that there's something on the moon that makes us question our place in the universe. You can't let Joe Everyman know about whatever it is, there'd be immediate wars and rioting and market failures, so we say "oh we don't need anything on the moon, it's too expensive, there's no reward, we don't care," and we destroy footage and swear some people to secrecy at risk of death, and we never ever ever let anyone else in on what's going on. No new astronauts to discover the truth, no NASA employee briefings on it, so over time anyone directly exposed to the horrible information dies/retires and new people just think it's crazy conspiracy nonsense.