Update: So what is it? Why is Central America popular but South America is not? My guess is that "archeology" has always been mostly about digging up "gold and jewels". Since the Spaniards took away the gold from Peru, there is no more incentive to dig it up and report on it. Could that have anything to do with the lack of archeology today in Spain?
To be fair, looking into your ancestors is an important reason to do archeology, and it helps explain the large volume of stories about England, Italy, and Greece and Biblical areas.