For 50 years of American pride! Those special effects were decades ahead of their time, by 1969 standards! A few slip ups here and there (incongruent shadows/lighting, one of the prop rocks upside down), but by and large an absolutely outstanding job.
One of the few mistakes. Flag's shadow is unfortunately absent. Or in the wrong direction, depending on your perspective. But mostly pretty good, Mr. Kubrick.
Another minor Kubrick mistake. The lunar leg shows two shadows. One going toward the astronaut. And one going at a 90 degree angle. It's tough to get the appropriate lighting with just one light source (like the sun).