The pictures of the Earth from Apollo were not full Earth because of the lighting conditions needed on the moon for the landings. It was desirable to land just after sunrise at the landing site on the moon, so the shadows of craters and boulders would make them easily visible to the astronauts. This meant that the sun was coming from the side on both the Earth and the Moon and the Earth would not be fully lit as seen from the moon. I guess Apollo 8 just happened to occur at such a time only because they were trying to beat the Russians to the moon, and fit in that time period. I don’t think anyone was thinking of lighting conditions to photograph the Earth then.