Our legal philosophy concerning corporations is "perpetual life," which means it lives until it goes bankrupt (so essentially, it can live forever). The crimes a corporation committed 140 years ago are still relevent today, and so long as the property of its owners and managers isn't taken away (which it cannot be, by law), you're only punishing the corporation. It's somewhat of a difficult approach to comprehend, but it takes back the money that was earned by means of slavery, though it takes it only from the corporation, not from people.