"One small step for man one giant leap for mankind" - Neil Armstrong
In July 20 1969, Neil Armstrong and Buzz Aldrin landed the lunar module Eagle on the surface of the moon. Apollo 11was the space craft which carried the 2 astronauts. After 6 hours of landing Neil Armstrong was the first human being to set foot on moon.
After Apollo 11 so many Apollo series spacecrafts reached moon with humans. On 14th December 1972, Eugene Andrew Cernan was the 11th and last person who walked on the surface of moon.
According to some news reports US took some short route to reach Russia as it was also preparing for space missions. The priority was to beat Russia and not to build a clear path to Moon.
The reason was oil crises during 1973 and due to that funds allotted to space research was reduced.
And the cold war between Russia and US were no longer seen, the importance of showing superiority is no longer in the agenda.
And space researchers were interested more in space stations and satellite launching for the improvement of human life style and knowledge than in Moon.
Life in Mars is more appealing and possible than the results of Moon missions.
And US concentrated more on war against terror than going to Moon.
Even after 46 years NASA is not interested in Moon Missions. May NASA doesn't have evidence that Moon Missions will be any use to humans.
These are the possible reasons for the doubt, why didn't NASA return to the moon.