[fastball]

Shuttle itself was refurbishable, but not rapidly re-usable. It was also incredibly expensive to build and refurbish. A shuttle launch also utilized boosters that were not re-usable.

Starship is supposed to be (and clearly well on the way to being) fully rapidly re-usable. That means all stages (in this case two) are re-usable, and that the capital and time required to get either stage flight ready again after a flight should be minimal.

Said another way – it is cheaper for SpaceX to build an entirely new Starship + Booster than it was to refurbish a Shuttle between flights, by a factor of about 4x ($90M for a Starship+Booster / $400m for Shuttle refurb).

[fpoling]

The boosters for the Shuttle were reusable, but it turned out the cost of refurbishing them was similar if not higher than simply building new ones. Plus it contributed to the Challenger crash, see "Mr. Feynman Goes to Washington", https://calteches.library.caltech.edu/3570/1/Feynman.pdf