The OP is confusing the use of volume in a/b demonstrations (where listeners will often prefer a subtly louder replay of a track) with listening levels in general.
I have never seen in print or heard an assertion that a majority of people prefer louder playback on a sustained basis.
On "loudness", there is quite a variation in the levels that different recordings are mastered at so even listening at a consistent average SPL can require quite different volume control settings.