system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why hasn't anyone been back to the moon?
gpt
The infrastructure to land on the Moon costs a lot up-front, takes years to develop and build, and the missions are all very politically risky for those who support the program.

It took a long series of coincidental things to prod the US government into funding and continuing the Apollo program.  It came close to being canceled over and over during its time, but lucky breaks (sometimes tragically ironic ones) kept it going.  

Kennedy was looking to cancel it in favor of a joint mission with the USSR that probably would not have been funded, but when he was killed, Apollo became his symbolic legacy that LBJ doggedly pursued.  Then the Apollo 1 tragedy revealed all sorts of technical problems that would have made the schedule impossible if they had been neglected, and added three more bodies to the list of sacrifices demanding completion.

A perfect storm of factors had to occur to make the program work and remain politically on track, starting with a nation with unprecedented surplus wealth feeling insecure enough against a competitor to plow massive amounts of that wealth into achieving victory in a symbolic competition.  

It was a lot like what happened in the Renaissance, but on a much huger scale.

Such combinations of factors are rare.