The most watched event at the World Championships were the men and women's sprints 100, 200 and 400. As one example the mens 100M was the biggest draw with the largest audience of the games. Because people do some sort of distance running as part of their fitness program does not mean they are interested in watching someone go round and round a track repeatedly. It is inherently boring while sprinting brings instant gratification. Sprinting is sexy which is why sprinter's get bigger endorsement contracts than distance runners. Middle distance running up to 1500M has some element of drama but beyond that the general public cares little for distance running. It is just a fact of life.