I think it might be worth flipping the question around, why do you think it was a genocide? The war ended with the destruction of the city of Carthage but not the Punic people, very nasty things happened to the people of Carthage but the city's sack was not followed by a prolonged policy of extermination, and there was no real population policy included in the conduct of the war or its aftermath. How are you defining genocide and what characteristics of the Third Punic war match that definition?