Why does NASA not go back again the moon after 1972 ?

Between 1969 to 1972, NASA reported that their space plans let astronauts landing on the moon successfully for six times.


In this 40 years more, why do they not go back again ?

Is the reason of technology not enough ?
I don’t think current technology will be poor than 1969 only if the technology in 2017 is still not enough confident to let astronauts land and leave safely !

If it is not related on technology issues, what other reasons to let them stop it ?
Money ? I don’t think so, they can use back 1969’s technology and hardware that are already enough.

Or they found the moon is not a planet only ? or they had seen something which let them afraid of it ?