It could be that they are persons of interest to the FBI, also the FBI maybe not sure where they are located and flag a everyone by that name, for example if there is a person called Khalid Shaikh mohammad who was the number 3 guy in Al Qeada everyone in the world with that name has been flagged which increase the list.
Have you actually taken the time to visit the link Bernard posted and had a look at who has been put on the list? It's all a big sham that has been implemented to keep people like you living in fear of your own shadow.