Why People Walk Away From Omelas

This story is built with the reader in mind. You, the reader, are involved in creating the world to some degree, I believe this serves two purposes. The first is to create a more vivid image of the town in the readers head, you can pick and choose what parts fit within your imagined view of the city and which ones do not. Details like allowing the reader to add transportation of their liking builds on the current structure of the town outlined by the author. The other reason for allowing the reader to sculpt the city is to include them in the horror outlined in the latter half of the story. In building this city the reader becomes complicit in its underlying corruption.
The inclusion of the child locked in the cellar is very precise, the reader is not allowed to change this place like they were in the town above. By doing this, the author makes it imperative that the child receive poor treatment. It's sacrifice makes it all the more outrageous to the reader
What I would also like to know, is why the others stay. It is only revealed that some people leave the city at the end of the story, because of the proximity to the story to the child, it has to be assumed the child is the catalyst making people choose to walk away, otherwise there could be any number of unrelated hypotheses. I believe the people walking away are ashamed. They cannot stay within the city because they feel guilty for the child but they know they cannot let it free because it would bring the guilt into the entire city, thus deflating its happiness. They leave the city in order to escape the shadow of guilt and to allow the happy city to go on. The people that stay within the city know of the child's existence but they choose to ignore it and go on with their lives, if the feeling of guilt overcomes them, then they must leave or risk destroying the city and making everyone