It’s a customary practice, and I think it’s a good one because it makes the story less one-sided and can diminish the appearance of it being a hit piece if it’s negative. Bottom line, it’s natural to want to know what the person the story is about thinks of it and what their perspective is. Obviously not all journalists seek a comment from every subject, but if they do, they often mention that they asked for a comment even if they weren’t able to get one, because people want to know that they at least tried.