Unfortunately, NASA acted for 25 years as if it’s primary goal was to validate President Carter’s claim: “The space shuttle is just a contrivance to keep NASA alive” – SciGuy/Houston Chronicle.
The common sense route to a robust, low-operations-cost, fast-turnaround, fully reusable space transportation system would have started with small experimental vehicles and worked up from there to solve the myriad little and big problems facing development of such a system.
NASA, however, required a big program to support its infrastructure and workforce that remained quite big even after the painful budget cuts following the end of Apollo. Like building a 747 in 1947 on a 1937 budget, NASA went with an over-sized (to get DoD support) and under-funded (to keep Congressional support) vehicle that proved to be both extremely expensive and fragile. The average cost of a Shuttle flight was over a billion dollars. This in turn made building the ISS extremely expensive and drawn out. Furthermore, it left no money for development of an in-space transportation infrastructure (e.g. space tugs, fuel depots, etc.) and nothing for deep space human exploration. Nevertheless, right up to the Columbia accident NASA officials were talking about flying the Shuttles until 2030.
The new heavy lift vehicle program is yet another contrivance to keep NASA living the way it always has – a big program to support a big agency with enormous overhead and fixed costs.