The other reason for the 6 landings was that each was accomplishing something different. The first was just to get there.
The second was: First precise manned landing on the Moon. Recovered part of Surveyor 3 probe. (They wanted to study the effects of the extended duration on the probe)
The third was a geological survey to the Fra Mauro formation.
The fourth was “the first of what were termed “J missions”, long duration stays on the Moon with a greater focus on science than had been possible on previous missions” and the first with a lunar rover.
The fifth was another “J” mission, with an exploration of the Descartes Highlands, and a subsatellite used for magnetic readings
And the final landing brought an actual scientist along, and did a whole lot of geological surveys. The geologist was also a bit of a goofball, if you watch the videos =)
Each landing learned something new, and the moon isn’t homogenous, you couldn’t just take what they learned in the Sea of Tranquility and apply it to the highlands (which they thought, originally, were volcanic in origin, turn out to be impact origin)