Why is Everyone Running a Marathon?

In 2003, it took over 8 months for the Chicago marathon to sell out. In 2011, that time length was down to 31 days. And In 2012, it sold out in only 6 days. Perhaps it's not with surprise that the Chicago Marathon sold out in just a few hours in 2013, accompanied by technical problems that suspended registration for 2 days. The race has since moved to a lottery system, along with a few others including the Berlin Marathon.

Chicago was established in 1977 and one of the 5 world marathon majors, among Boston, London, NY and Berlin. The marathon as a race has been around for centuries.  

So why all of a sudden are we seeing huge increases in registrations and sell-out rates? 

Surely with improvements in health research and awareness, there is more emphasis on healthier lifestyles and daily exercise, but national obesity rates continue to creep up (~30% of the US).  As you can see from the chart below, the # marathon finishers has steadily increased over the past 30 years, as running grows in popularity and new races are launched.

I speculate that the rise is largely due to social networks and the ability to easily share intent with family and friends.  The event itself can efficiently market to today's tech-savvy runners as advertising moves away from TV & print to online channels. 

A few other interesting stats about the Chicago marathon: it creates $150million of economic activity, ~1k jobs and $70million+ for charities.  Maybe it shouldn't happen only once a year!