The Shuttle was intended to wind up as the ONLY launch system at its inception, and expendables were headed for the scrap heap. This included military launches of large spy satellites into odd orbits, which drove the winged shape for high cross-range and the huge payload for military and ISS applications.

A more sensible multi-vehicle solution, some expendable, some reusable, would have been cheaper overall, and the move to complete reusables less drastic and more useful.

For example, a large conventional rocket with its engines, avionics, and other expensive items in a reusable "pod" at the bottom and expendable propellant tanks drops launch costs quite a bit, but is far easier to develop than an SSTO.