That's a bit of a simplification, I think. The status quo benefits South Korea as well - reunification means absorbing crumbling infrastructure, 25 million undereducated and hungry people, and trying to integrate that with a technologically advanced economy. It'd make the costs of the German reunification look like nothing.
It benefits everyone who isn't a citizen of North Korea for the current regime to stay in place.
South Korea is afraid of sudden/violent collapse of the NK regime for such reasons, but South Koreans are overall in favor of eventual peaceful reunification (though I think enthusiasm for reunification is fading somewhat over time, as those with personal connections to people in NK die)....
It benefits everyone who isn't a citizen of North Korea for the current regime to stay in place.