Congress cut NASA’s budget. NASA’s response should have been to dump the plans for a quasi-reusable vehicle, but of course it didn’t, it pushed even harder for it, and dumped every other proposed project. The Air Force wasn’t interested in it without an increase in payload capacity, which meant a larger vehicle, which meant SRBs.
The interesting thing about the SRBs, which are often complained about by, well, idiots, is that they are reusable components, and in terms of bang for the buck, they actually make the most sense. In the upcoming SLS enhanced versions will make their return to man-rated vehicles.
As disposables.
Four of the existing-design SRBs could send a manned lunar mission into direct ascent trajectory to the Moon — no shuttle, no liquid fuel first stage engines, just light and go. That could be designed in a couple of years, and launched to the Moon by 2020. A single SRB costs about $50 million new, the estimated cost of recycling that I’ve seen is $18 million per SRB per launch. IOW, even if the four-segment SRBs used on the Shuttle were put together for a lunar mission, and thrown away, it would only run about $200 million for the first stage; if recovered, the cost for subsequent missions would drop below $60 million for the first stage.
Von Braun never worried about reusability, he understood the tyranny of the mass budget. He wanted to use the Saturn V boosters to assemble Mars missions in orbit. His vision would have led to twelve Saturn V launches to assemble a single manned mission to Mars.
The shuttle was a quasi-reusable vehicle. NASA failed to focus on optimizing the availability of the system because they were desperately trying to get something past Nixon’s idiot bean counters.
And it is simply false to say Von Braun did not care about reusability. He didn’t have time to develop it in Kennedy’s schedule. He envisioned a stepwise approach that would have developed a reusable spacecraft and space station as infrastructure for getting to the moon.