The green zone came from a request from the refugees themselves. Once again, many of the internally displaced persons don't want to leave their homes. Nobody wants to leave their home. Some of them have found that their lives there are absolutely impossible at this point. They have a stigma against them. They're persecuted, and that persecution does not stop. The Kurds are unable to protect them. The Iraqi soldiers are unable to protect them. The Shia militias within the Iraqi army are not protecting them.
So the idea came to have the immigration option and/or to have a green zone where the refugees could be protected if they chose to stay in their homeland. But if they chose to leave, they would be free to request to be refugees.