A modern piano is a matter of iron and steel and high-tech and some degree of assembly line. In the days of Beethoven and Schubert, it was a matter of one man or woman (such as the legendary Nannette Streicher) with hammers, saws, planes, and chisels, and there were myriad visions of what a piano could be.
Here's Alfred Brendel playing the beginning of the "Moonlight" about as well as anyone on the ubiquitous modern Steinway.
Compare that to Gayle Martin Henry playing a piano from around 1805 by the Viennese maker Caspar Katholnig.
The sound is startlingly different from a modern piano and takes a while to get used to. These instruments were mostly played in small to medium-size rooms. The sound is intimate; you hear wood and felt and leather. The voicing is varied through the registers rather than the homogenous sound of modern pianos.
Even a physical object can feel less rich, organic, or alive, when industrialized instead of hand crafted.