Marathons are stupid
Marathon running has a certain glamor and status to it. It shows that you are disciplined, tough, and (probably) extremely healthy.
Everyone forgets that the first Marathoner in Ancient Greece completed his marathon and promptly dropped dead. Extreme distance running puts a ton of stress on the body.
People need to approach these long races with the understanding that it is ok to stop if their body tells them something is wrong. Unfortunately, having been an endurance athlete myself, the tendency to "push through pain" is engrained in you and becomes part of your self-identity. It is part of the allure of endurance sports, that you can gut through something longer than anyone else.