As Dr. Mortimer said, "I am telling that which I have not confided to anyone. My motive for withholding it from the coroner's inquiry, is that a man of science shrinks from placing himself in the public position of seeming to indorse a popular superstition. I had the further motive that Baskerville Hall, as the paper says, would certainly remain untenanted if anything were done to increase its already rather grim reputation." Or in other words, he had 2 motives.1. He is a scientist, he doesn't want to support a superstition that has no facts.2. He was certain that if this came out, no one will want to live in the House of the Baskervilles again, and its already grim reputation will become terrifying, no one will want to be there, much less live there. I hope I helped!