Because you still need to build and launch a rocket, even if it doesn't go to the moon or carry the actual crew, it needs to at least go over the horizon convincingly enough.

All that design and construction still needed to be paid for.

Presumably faking the capsule return is cheap enough if you drop the capsule out the back of an aircraft.

Faking lunar return samples, returning signals from orbit for the various ground stations around the world, and a variety of other things also required a lot of deception, too.

Then, ofcourse, you have to hope that the Russians didn't put out a headline of "Americans fake lunar landing". Since they kept a close eye on things.

Because all of the technology and machinery necessary to go to the moon was designed and built. The massive and massively expensive Saturn V rockets(many of them) were designed, built and launched to witnesses. The LEM, CSM, suites, computers, and etc were all built. The simulators were built and simulations run. Etc and etc and etc; hundreds of thousands of people invovled.

So, pretty much all the cost of going to the Moon and now add on the cost of faking it and maintaining that lie for 50 years.

And they would know that "maintaining that lie for N years" would prove useless as soon as the powerful cameras in lunar orbit would photograph the landing sites. Who would participate in such a lie knowing 100% it will be exposed, eventually...

I remember reading an article years ago, saying that it’d have required the invention of electronics that did not exist yet to slow down the footage (simulating 1/6th g) and pull off a live broadcast that lasted hours and hours. So in essence, it’d have been the more impressive thing to do technologically speaking. Having seen the new 1 hour documentary on Apollo 11 and how rickety everything looked and barely worked, I’d agree with that assessment.

You may be thinking of this video: https://www.youtube.com/watch?v=_loUDS4c3Cs

Edit: changed to earlier upload of same video

This is very informative presentation. Thanks for the link.

Because it's a lot more than just a movie. Millions of people witnessed aspects of the program in person over a 10-year period. The workers, their families, and the public. You'd have to spend enough money to fool all of them.