> After the Shuttle program ended in failure, work on reusable launch systems stopped for decades

Did it really stop for decades? I think SpaceX and Blue Origin were both already working on re-usable launch systems around that time

After the Challenger disaster (1986) it was clear that the Space Shuttle was never going to accomplish its cost and reliability goals. The US military had bet everything on the Shuttle, so it needed a new launch vehicle. The one clear requirement of the new launch vehicle was that it had to be expendable. In fact, the name of the program was "Evolved Expendable Launch Vehicle"[1]

Remember also that when SpaceX started to develop Falcon booster reuse in 2011, every major aerospace company said that reusable vehicles would never make economic sense. Even after the first Falcon 9 recovery and re-flight, most aerospace companies thought reusability was a dead-end and that belief came from the refurbishment cost that Shuttle had to go through.

I count from 1994 (start of EELV) to 2021, when NASA launched astronauts on a reused booster and Peter Beck famously fulfilled his promise to eat his hat if Rocket Lab ever worked on a re-usable launch vehicle.

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[1] https://en.wikipedia.org/wiki/National_Security_Space_Launch

SpaceX started with the business plan of low cost, mass producible single use launchers. Falcon 9 was not designed with any level of reusability in mind. There was a major redesign to add landing hardware, but the whole reason for Starship being a totally new design was the reusability that a Falcon "super-heavy" derivative could never achieve.

In the 80s, the reusable spacecraft people got sidetracked into SSTO designs, which have horribly small payload fractions. The Delta Clipper and DC-X families were meant to be reusable, but they never scaled up to something that could deliver decent payloads to orbit.