Topical coatings are sold as an easy answer to dull stone, and they do look convincing at first. They are also a layer of plastic sitting on the surface, and they wear through where people walk. The result is glossy at the edges of a room and cloudy in the traffic lanes, and it cannot be spot-repaired because the boundary between worn and unworn always shows.
Coatings also trap what is underneath. Moisture, staining and previous damage are sealed in, and the stone stops behaving like stone — it can no longer breathe, and on some substrates that causes further problems.
Multiple layers accumulate over years as each failure is answered with another coat.