IIRC, there were still-born plans for Shuttles to 'burn the tank dry' and carry it into orbit.
Sundry snags included the weight overheads, the severe restrictions on payloads --Flown Shuttles ran rather heavier than hoped-- and that pesky, crumbly foam. Then they'd need multiple space-walks to clad the exterior in reflective 'bumper' layers which would have to be hauled to orbit. Then there was the weight of space-rated hatches and connecting tunnels, which would have to be hauled to orbit and retrofitted due to their materials' incompatibility with cryo-stuff...
Oh, and the tankage was full of baffles which would need to be removed without leaving sharps...
Given a *real* space station and routine spacewalks, all of this would just take work. Given the limited shuttle fleet and their modest endurance, plus the 'too-little, too-late' ISS build, it was a non-runner...
IMHO, had Skylab survived to form the nucleus of a space station, the different outlook might have changed things. Perhaps, but probably not. IIRC, Skylab was seen as 'old tech', 'Apollo stuff', unfit for the bold, new Shuttle era. Of course, having painted themselves into a corner, NASA discovered that the Shuttle just could not deliver on time or on budget...
