The space conquest spirit disappeared along with the conquest spirit in general. Without a great power struggle like the Cold War, the motivation simply hasn't been there do anything on the scale of Apollo again. This the great irony of the human condition that I as a Sith find so amusing: strife is the source of so much of our progress, yet "progressives" always strive to make peace. As Harry Lime put it in The Third Man:

“In Italy, for thirty years under the Borgias, they had warfare, terror, murder and bloodshed, but they produced Michelangelo, Leonardo da Vinci and the Renaissance. In Switzerland, they had brotherly love, they had five hundred years of democracy and peace – and what did that produce? The cuckoo clock.”

Many of you are probably too young to understand that there has been a great cultural deconstruction over the past 50 years which has moved Western nations away from higher "imperial" visions toward more mundane ideals like equality, GDP growth, peace, technological progress and a hedonistic ethos. As Peter Thiel put it, "the hippies won," and the falling out of favor of von Braun, et al's "conquest of space" ideals was one of the first casualties of that defeat.

Old school civilization theorists usually associate the onset of liberalism with the declining or terminal phase of a nation, when it no longer has any strong ethos, vision or sense of collective destiny. Space could/should have been our collective destiny, but it seems that other ideas prevailed, and now we all may have to live in the ruins of that ideological failure. Meanwhile, in rising nations like China, the imperial spirit is returning and they are showing the kind of energy and cosmic ambition that the West had prior to our cultural deconstruction. Their space program is proceeding methodically according to a long-term vision, and there is no reason to doubt that they will own the Moon and Mars by mid-century. In my view, the West's liberalism and lack of a great enemy has been our undoing in space, and our democratic capitalism has been discredited as a system capable of sending mankind to the stars.