Because who cares about the 2nd mission that landed on the moon?
- Apollo 8: 1st time a human being saw the dark side of the Moon
- Apollo 11 : first man on the moon
- Apollo 13 : human miracle
- Apollo 17 : last man of the moon
The other missions... the general public does not really care. Eventually some people would like to add Apollo 15 because of the lunar rover but that's it. Tintin's comics about the Moon probably have a bigger impact on population than any Apollo mission expect 11 and 13.
edit: any space mission expect those 2 above, Sputnik, Laika and Gagarin in fact...