North Korea and South Korea are still technically at war, yet both are fighting for the same thing - the reunification of the Korean Peninsula under one government. While its clear to the rest of the world that North Korea is a failed state, the North still believes it has a chance to be victorious. South Korea, if it truly desires reunification, must take steps to reconcile with the north.
South Korea is in a rather difficult situation because they share a border with North Korea. If you're not familiar with North Korea, they are the country whose leader, Kim Jong-un, just executed his uncle and is only willing to negotiate with the United States' lead diplomat, Dennis Rodman. Yes, that Dennis Rodman.
South Korea HAS to find a way to deal with their unpredictable neighbor. The Sunshine Policy was a worthy attempt to improve relations. The only thing worse than a crazy neighbor is an crazy neighbor who is angry at you and has nuclear weapons. South Korea has little appetite for another Korean War and attempting to engage the North to ease tensions was worth a try.