Lets be honest.
a 3 hour marathon is equal to about a 14 second 100m.
Or a 6 minute mile.
Hell a 73 year old with cancer ran 2:54.
Its a jogger's event. Distance running is about as uncomplicated as can be. Just put in the miles, control the boredom. Go hard when you have to.
Percentage wise there are way more people who could run a 3 hour marathon, than say a 12 second 100m. Its an endurance event, at sub maximal levels. A sprint is at maximum efforts with technical difficulty, and the chance for injury.
The danger in a 3 hour marathon is falling asleep on the road.