Because the instrument (piano) is as percussive as it is melodic & etc. Can be, or becomes very 'is', when under the proper pair of hands.
In this instance: Equal measures of delegating and elegating. Letting the others have their say; while just hanging back, and punctuating from the periphery. A diffusion of hammerings. Asymmetrical counterpointage, vs. a guiding beacon vaguely sighted through fog. The sound of mirrors and purviews splintering apart, and then coming (being brought back) back to together again, many times over, each time as if nothing happened when you weren't looking/listening.