African gold brought wealth in ancient times, and the darker skinned Nubians became invaluable trading partners to the ancient Egyptians; living around Aswan in the south, they remain close to their roots and their strong musical traditions.
Nubians had an vibrant, ancient trading business with Egypt.
One answer is that there is no honor among thieves--that the oligarchs are caught in a classic prisoners' dilemma, in which it is in the collective interest of the group that everyone pay some taxes, but in the individual interest of each oligarch to free-ride on the others.