Why do singers keep returning to the same handful of old songs?
A standard is not a fixed thing to be reproduced but a frame to be re-read — the same harmony and lyric giving up something different in every set. The interest lies less in the tune than in what a singer decides to do with it: where to lean, what to leave out, how to answer the band.
There’s an example close to hand — a rehearsal reading of Ellington’s ballad in Prelude to a Kiss.