Here's an hypothesis. The sound of acoustic instruments is nearly unknown to most people. Rarely do we ever hear instrumental music, and especially vocal music, without amplification. To make matters worse, most of the time we hear music through mediocre to poor PA systems at higher than natural SPLs, and often ridden with distortion. When we actually hear clean, clear, low distortion music, it's such an anomaly that it doesn't quite "sound right." The shock to our ears has us longing for a more "natural" sound, not too much, not too little, but just the right amount of distortion. The Goldilocks sound of tubes and LPs.