Mostly the heavy steel booster cases were reused, iirc. I don’t believe the reuse process was ever cost-effective. As for the Shuttles themselves, so much inspection and refurb was required that it made reuse look unattractive.

SpaceX is getting the entire first stage back in mostly flight-worthy condition. Nobody outside the company truly knows how much work is done between flights but it appears to be vastly less than Shuttle.