[xavxav]

Another key factor: NASA has no control over its funding (and thus vision) it’s at the mercy of congress each year which makes planning and financing large projects hard. They have projects and designs imposed from above regardless of the scientific or engineering benefit.

[cameldrv]

Perhaps the tragic reason for NASA's success in the 60s was Kennedy's assassination. Kennedy set the goal and the deadline, and after his death, it could not be revised.

[shiroiuma]

Perhaps his death was faked for precisely this purpose, by aliens wanting to make sure humans made this important step in space travel.