Why were so many Americans treated by their government as though their lives were as disposable as facial tissues? Because that was the way authors customarily treated bit-part players in their made-up tales.
Classical stuff takes a lot of rehearsal time and preparation, but with stuff that involves improvisation, you can over-rehearse it and it gets stale. You don't want it to be too comfortable. In fact, a good sound check, a good rehearsal usually means a bad performance.