Even if we assume the whole fuselage is intact in one piece, with the wings broken off, it's possible that it fell into the mud, silt and soft squishy bottom on

Even if we assume the whole fuselage is intact in one piece, with the wings broken off, it's possible that it fell into the mud, silt and soft squishy bottom on some abyssal plain and is more than 1/3rd buried. Making it even harder to locate than a cylinder resting on a rocky surface.