I would think that a main purpose of sending slow-scan video from Apollo 11 was just in case the spacecraft and astronaughts didn't make it back to earth (along with the high quality film moves and film stills), NASA would have some moderate quality record of the flight, by means of the slow-scan transmitted images.

But once the 16 mm films and 2-1/4 stills made it back, that would lower the long-term value of having the slow-scan video.