So stereotypes persist because we want them to?

That's one answer. But the second answer to the question of why stereotypes persist despite contradictory experience has to do with how we think in generalÑwhat psychologists call our cognitive processes. While the brain is a powerful information processor, it is not perfect. The brain operates in a way to achieve probable accuracy, not perfect accuracy, and certain kinds of errors or "conceptual illusions" are preferred over other errors.