Not to mention the sheer logistics. I had a buddy who worked in TV production for years, and he used to laugh at people who thought faking something like that would be easier than just doing it. He once told me about a small commercial shoot they did, just a 30 second spot with maybe 20 people on set, and even that was an absolute nightmare to coordinate. So when @abbyd36 points out the thousands of people and all that technology involved in the Apollo missions, it tracks perfectly. You'd need an army of people just to keep the lie straight, and somebody would've cracked eventually. It's way more work to build a convincing fake than to just go do the thing.