You've got a lot of responses on the difference of reusability, but the shuttle was also more expensive because it had to carry a lot of capabilities with it every time. If you were launching a satellite, you were carrying along the crew compartment and a couple astronauts. If you were bringing a few astronauts to the space station, you brought a cargo bay. And in either circumstance, you brought big wings. Starship can be filled with all cargo. And if you're just changing crew on the ISS, you could... not use Starship and launch a Falcon 9 instead. One of the mission profiles required by the Air Force for the shuttle was that it be able to rendezvous with a satellite, put it in the cargo bay, and return to Earth, all under 2 orbits and along a path that avoided flying over the Soviet Union, which required a rather large turn in-atmosphere to make it back to landing on the west coast.
One of the drivers was the need to Abort Once Around on a polar orbit launch from Vandenberg. The launch site rotates to the east during the orbit so cross range was needed. No such polar orbit launch (abort or otherwise) ever occurred, though.
