Actually, the reason Apollo wasn’t sustainable beyond the first few Lunar missions is because it had no objectives beyond that. Once the United States demonstrated technological dominance over the Soviet Union by putting footprints and flags on the surface and the public lost what interest it had (which was never more than 50% approval at any time during the program) the program rapidly coasted toward dissolution, to the point that even proposals to use spare hardware only resulted in the Apollo-Soyuz Test Project and the abortive Skylab, with several Saturn V flight sets and Apollo CSMs virtually complete scrapped or used as display pieces.
It didn’t help that Nixon had zero interest in continuing a program started under Kennedy and heavily promoted by Johnson, but the fact that it had no real goals beyond slightly longer Lunar J-class survey missions and no planned infrastructure for a sustainable human presence in space meant that beyond keeping contractors pockets full of cash there was no impetus to continue the program. Space Transportation System (“Shuttle”) was started primarily to keep the contractors employed, but lacking a space station to support it had few dedicated mission needs, hence the decree that all government satellite launches would be by the Shuttle program even if it made little sense to do so, and the abortive and costly “Blue Shuttle” program in which the USAF would borrow NASA Shuttles to be flown from Vandenberg AFB out of SLC-6 before the Challenger disaster put an end to Air Force interest in being involved in Shuttle.
Apollo was a very fast, highly integrated program; I woudn’t quite call it a “crash” effort, although the artificial decree that Kennedy set for landing men on the surface of the Moon did result in taking on a lot of risk that would be unacceptable by modern safety standards (and rightfully so). There were technical experts giving the Apollo XI mission only a 50% chance of success, although what the actual basis for that was I cannot say because the system was so complex that reliability estimates would only be guesswork.
Meanwhile, uncrewed programs have visited every planetary body in the Solar System, have increased our knowledge of planetology and astronomy by orders of magnitude, and have cost a tiny fraction of the crewed program efforts which are largely concerned with just keeping human astronauts alive and marginally functional. The Mars rovers, and especially Curiosity and Perseverance, are marvels of compact and reliable technology, and the Voyager, Galileo, Ulysses, and Cassini-Huygens missions have collected information we could never have achieved with human exploration. I knew crewed exploration gets space enthusiasts’ juices flowing but on a scientific value per dollar basis crewed missions are like owning a yacht; you are basically just throwing bags of money in a pit and setting it on fire.
Stranger