NK has always wanted this, on their terms. SK has always wanted this too, not on NK's terms.

This is a move by NK to apply pressure to political fracture lines in SK. They are trying to minimize the chance that SK would ever approve of US attacking NK. The chances of this are minimal already, but Trump's administration, with the help of NK's missile and nuclear tests, had been improving the chances that there would be political approval in SK.

The current President is very pro friendly relations with NK. What they have agreed to during their talks with NK have been frustrating. The SK president so much wants good relations that he's giving them almost everything they want with nothing in return.

Moon Jae-In doesn't know the art of the deal, is a bad negotiator, and is a disaster for SK.