Agaiambo
The Australian soldiers were flying over a crocodile-infested swamp in the Oro Province called Agaiambo. It was in this swamp that they spotted the missing aircraft. That would probably explain why it took so long to find this aircraft.
photojournal.jpl.nasa.gov
Simply put, the Agaimbo was in an extremely well-preserved area, meaning not even tourists or locally accessed the area much. It used to be home to a group of marsh-dwellers called the Agaiambo/Agaumbu but were now considered extinct. Other than these people, nobody else lived in the area.