Community value
Lots of people think running is a silly avocation. Running marathons, they believe, is wildly eccentric.
So, some marathon organizers (and other race directors) try to find ways for non-runners to relate to their events. They may support a charity, although that gives the race, more than the participants, a valued connection.
Some, like the Bank of America Chicago Marathon, publish stories about regular people who run the race. Some run for charity, some for personal satisfaction, some to achieve an important goal.
Remember that only 4% of the public runs regularly. Less than half of those race, and only a small number of those race in marathons.
So, to bridge the gap between runners and everybody else, it helps to promote an aspect of the race that has value to the general community.
Folks may still scoff at the idea of running, but they'll be more likely to value and respect the runners.