There's that but also NASA gets continually screwed with, the moon return mission changed scope every 8 or so years when a new president came in and wanted to put their own stamp on the project to claim it for themselves.
It's slightly less cynical than that - it takes about eight years to design a space mission and rocket, but doing the detailed design is expensive as hell, so in order to meet a budget, they then change the mission, so they can go back to the vastly more affordable task of talking about doing work, vs doing work
