Often, especially now with the 50th anniversary of the Apollo 11 mission, the question is asked: Why did we stop sending people to the moon. The answer is usually: because the USA had proved they could do it and it is extremely expensive. The only reason so much money was spent on it was that the wanted to land people on the Moon before the Soviet Union did. Now the Soviet Union never did this, nobody else did it, so the moment Neil Armstrong set his feet on the moon, they had won that race. Why spent more money on sending 5 more missions. Why risk 15 more lives? Yes, they made some small other firsts, like the first moon rover, but nothing that impressive. Plus, if that was a reason to continue, they wouldn't have stopped after the sixth mission. There is so much more one could do, like digging a hole, growing a plant etc.
The only reasons I could come up with is that the main costs were made (research) and for some spare change they could add 5 more missions (I think this is the reason for a couple of Mars missions in The Martian). Or maybe NASA was afraid the first mission would fail, so they had already prepared for a few more attempts.