The shuttle SRB's were really only reusable in the same sense that the engine from a wrecked car can be removed, stripped to a bare block, bored out, rebuilt, and placed into a new car is reusable. Hard to say exactly how long it took to turn around SRB segments, but just the rail transport between Utah and Florida was 12 days each way. SpaceX has turned around Falcon 9 boosters in under a month.

And even with all of that, the most reused reusable segments barely flew a dozen times. There is one Falcon 9 first stage that has now flown 18 times.

You're not wrong about parts having been reused in the past but the scale of what has been done before really doesn't compare to what SpaceX does now.