I just finished reading the story and this was the question I was left with. I think it's the question you are meant to ask, for two reasons. The first is, we are looking at this world through our lens of freedom. The second is that we are all used to watching the protagonist start a revolution in these dystopian tales (Fahrenheit 451, Hunger Games, Repo Men, The Matrix, etc.)
The brilliance and possibly the entire idea of the novel was to tell the story of people who weren't that type of person. There are all sorts of people like that in the world. It's a trope in the genre to tell the rebel's story - but what about everyone else? I wonder how they might react to a rebellion...likely with distrust and disgust. That's the whole point of the story. They don't have the perspective necessary to incite inside themselves the idea of a rebellion. While you could rely on a sci-fi explanation of why a clone might not rebel, the more likely statement <PERSON> is making is about the human condition, and how injustice survives in the world.
I think that song is an important key to the whole ordeal. 999
Her favorite song is "Never Let Me Go," and yet she does nothing but let people go, especially the man she claims to love more than anyone - more than once. She doesn't even think of the song in terms of her own life. She never applies it to the situations she's actually in. I think we are meant to be infuriated with them for not running. But if you think about who they are as people, it just wouldn't make sense.
The whole story reminded me of the idea of frogs in hot water. If you put a frog in water and turn the water up slowly enough, it will remain there, never attempting to get out of the water, until it has been boiled. This is what is happening to the clones in the story. It's terrifying, but also very realistic. Great book. I was searching myself for some "explanation" of why they didn't run, but reading this thread made me realize that if they had, this story would not make the same point at all. 999