Here, while she did leave a lot of questions unanswered, the questions aren't critical to the story. The setting in
Never Let Me Go is close enough to our world that the leap he took is worse than the leap in
House on the Strand which is obviously fantasy or hallucination and doesn't need to make sense in some ways.
Sort of an
uncanny valley thing.
Never Let Me Go is too close to our world in so many ways that the little differences and unanswered questions are magnified making it feel worse.