I guess that's why the Space Shuttle was called the Space Shuttle: it dropped astronauts (and supplies) off at the ISS and then returned to Earth with the previous batch of astronauts (this seems to have been a typical "ISS mission": https://en.wikipedia.org/wiki/STS-105 - mission duration ~11 days; the commander, the pilot and two mission specialists flew there and back, while three mission specialists were dropped off/picked up). Whereas a Crew Dragon capsule stays attached to the ISS for as long as its crew is there, similar to (most of) the Soyuz capsules.
> As the Apollo program began to wind down in the late 1960s, there were numerous proposals for what should follow it. Of the many proposals, large and small, three major themes emerged. Foremost among them was a crewed mission to Mars, using systems not unlike the ones used for Apollo. A permanent space station was also a major goal, both to help construct the large spacecraft needed for a Mars mission as well as to learn about long-term operations in space. Finally, a space logistics vehicle was intended to cheaply launch crews and cargo to that station.
> The Shuttle was originally conceived of and presented to the public in 1972 as a 'Space Truck' which would, among other things, be used to build a United States space station in low Earth orbit during the 1980s and then be replaced by a new vehicle by the early 1990s.
Well, you could say that those plans were ultimately accomplished, although much later and in a different form: the shuttle was used to build a space station (the ISS - not in the 80s, but in the 2000s) and was eventually replaced by a new vehicle (again much later, in the 2020s, with an embarrassing gap in between, and the new vehicle looks much like the shuttle's predecessors - but still...)
This is mostly because NASA wants there to be an escape seat for every astronaut in case of an emergency that forces the evacuation of the station (or say, a medical emergency). Even if they want to relocate a Dragon to another port, everyone who rode that capsule has to get back in for the relocation, so they always have a way back down.
During the space shuttle era, initially this wasn't a concern as the plan was to have the crew stay in one module until a rescue vehicle could arrive, but after Challenger, there was an extra Soyuz for that purpose.
