Because they are. This is a flight-of-fancy, a science-fiction diversion that has no relevance to any real world politics from the last century.
Their "Nazis with a mind reader" scenario explains it perfectly; only a small minority of people were able to lie well enough to escape a regime with 1940s technology. Millions of other people were killed and the Nazis did not need a mind reader to find them. A modern authoritarian state with a mind reader is barely any scarier than a modern authoritarian state without one.