Because it would be nice to see what the experts think. Maybe we'll philosophize and discover how true is true, or learn about the various degrees of the topic. If we need a magazine quiz to tell us, then that may serve as a tipoff to the answer. Once again, it's wonderful to receive the answer from someone else. If nothing else, this information may serve to make the cost of the magazine more palatable.
Some quizzes use the appeal to love.
Ah, well, maybe this is just your time. A little introspection, causing us to look at ourselves in ways we haven't already, serves us well. While completing such a task is difficult, it's still good to check ourselves out once in a while. If we don't know how to begin, or if we find doing so a cumbersome job, then a magazine quiz might prove the right tool.