I believe Curtis waited to come to Oklahoma because he was more interested in documenting tribes in their original area. In the place where they had a connection to the land and where their ancestors had come from. He believed in the idea of the vanishing race and wanted to capture them as unsoiled by white settlers as possible. He pursued the idea of capturing them as they were not what they had become. He was known for editing out any traces of modern conveniences from his photographs. At times he even dressed the natives in clothing he possessed that they had no connection to just for the sake of making them appear as they were before settlers came. He wasn’t interested in documenting the assimilation of native americans into a modern society and therefore had no interest in coming to Oklahoma until after he had documented other tribes that hadn’t been relocated. It is possible he thought photographing the tribes that had been relocated would go against his belief in the idea of the vanishing race. Yes the tribes were in a completely different area than their ancestors were and they were being forced to assimilate into a completely different type of lifestyle but they weren’t vanishing. I think he was also interested in documenting each tribe and their respective rituals and in Indian Territory it was harder to get natives to perform their rituals as many of them had been converted to Christianity or their rituals were outlawed or were very regulated.