We are so used to see Greek and Roman sculpture with missing limbs, noses, and other crucial body parts that our brain easily compensates for the losses.
In paintings, even small losses visually disrupt and destroy the two-dimensional illusion of a three-dimensional world, and our eyes are immediately drawn to the damaged area. Maybe it has to do with the fact that restorations and reconstructions of missing limbs and noses are often readily visible and mostly unsuccessful, being stylistically incongruous with the original. In fact, replicas and forgeries usually incorporate major losses, as they would raise suspicion when too intact. In antiquity, most Greek and Roman sculpture was polychromatic, but many centuries of weather, burial, and restoration have erased all traces of the colorful pigments (although in many cases still visible under the microscope), and the resulting  aesthetic of monochromatic, white stone has become the prevailing taste. 18th and 19th century sculpture borrowed visually from antiquity (just as Roman sculpture appropriated Greek imagery), reinforcing our idea of perfectly white, glowing stone. Ironically, today, polychrome marbles would almost seem gaudy. There is a parallel in painting where strongly yellowed varnish was often associated with a 'golden glow', confusing it with patina. When Michelangelo's Tondo Doni at the Uffizi in Florence was cleaned - long before the restoration of the Sistine Chapel - people were initially shocked by the bright, candy colored palette. The same bold mannerism is now visible in the restored ceiling of the Sistine Chapel, where centuries of grime and candle soot had covered and obscured the fresco, rendering it dark, soft, warm, and fuzzy, usually positive attributes. In my opinion, the criticism of the restoration is misdirected, and the harsh appearance is only due to to the modern illumination with thousands of watts of light. Painted to be seen from a distance, and originally sparingly illuminated by a mixture of natural light and candle light, it would never have been subjected to the scrutiny of potent halogen lights illuminating every square inch for photography and reproduction.