Most people aren't really familiar with the history of the world, especially the period of time that would correspond to ≈ 30-50 years before they graduated secondary school. I assume this is because there seems to be a pattern where you just don't actually catch up to current events in many history classes.

Also expecting the average person in the US to be familiar enough with world events to even know who Nelson Mandala or Narendra Modi are, is a good way to have a bad time. I don't like it either, but as Carlin said, "think of the average person, now remember that 50% of people are stupider than that."