Contact tracking is probably useful at the beginning of a new outbreak when the disease is still isolated to a small number of locations. Isolating a few people

Contact tracking is probably useful at the beginning of a new outbreak when the disease is still isolated to a small number of locations. Isolating a few people might prevent the disease from spreading to other areas. As you described, once an outbreak has a foothold in most areas, most people will be within one or two hops from someone who is infected. Also, the potential useful period will be shorter when the incubation period is long. Two weeks of incubation provides a lot of opportunity for someone to spread the infection.