Because one raced cars most of the world has deemed, and some still do, as primitive and barbaric, and while yes he won many championships, he ran almost exclusively in a single nation, one that in and of itself considers the sport a waste of time and money. The other raced in some of the most advanced racers on the planet, at very different circuits around said planet, and was one of the faces of the many series he was involved in, the biggest being the undisputed pinnacle of motorsport be it as a driver or an organization.
Be glad NASCAR was given any attention, and be grateful the Aussie V8's weren't chosen instead.