The third person limited point of view picks one character and follows him around – in this case, Mr. Utterson. However, Mr. Utterson’s point of view is supplemented by four other narratives: Mr. Enfield’s story of the door, the maid’s account of the Carew murder, Dr. Lanyon’s story, and Dr. Jekyll’s confession. We get the story this way because it draws out the suspense, and the mystery, and the shocking nature that was sort of requisite for shilling shockers back in the day. If we just had the story from Jekyll’s point-of-view, there wouldn’t have been such a dramatic ending, where we, the readers, get to say: "Ohhh."
Even though we hear other people’s perspectives, it is Mr. Utterson that we basically follow; we don’t learn the full story until he does. But since he’s a bit of a dry fellow – he must be, to spend so much time on religion and law – he’s not a terribly involved narrator. We watch him speculate about Dr. Jekyll and try to unravel the mystery, but he’s not overcome by strong emotions all the time. He’s an average fellow who cares about his friend’s well-being, and isn’t going to project many of his own opinions onto the story he unravels – which makes him a good narrator.