Partly because the South Korean president is a dunce, and partly or probably, because his translator is also a dunce. And if that's not the case, feel very sorry for South Korea.
From the AP:
As Bush began to wind down his stay at the Asia-Pacific summit, Roh challenged him to make a declaration to end the Korean War. That conflict ended in a truce in 1953, not a peace treaty, so the two sides technically remain at war...The story goes on to say that NoKo is technically at war with the UN, and last I checked Bush hadn't yet declared himself fuhrer of the UN. Secondly, I see no possible hurry to end an ongoing technicality without NoKo's complete cooperation down to the last disassembled and permanently deactivated nuke plant. Sounds quite reasonable to me.
Bush said that during his talks with Roh, he reaffirmed the U.S. position that Washington will consider the war formally over only when North Korean leader Kim Jong Il actually dismantles his nuclear program.
Whatever Roh heard Bush say through his translator, it wasn't good enough.
"I think I did not hear President Bush mention the - a declaration to end the Korean War just now," Roh said as cameras clicked and television cameras rolled.
Bush said he thought he was being clear, but obliged Roh and restated the U.S. position.
That wasn't good enough either. "If you could be a little bit clearer in your message," Roh said.
Bush, now looking irritated, replied: "I can't make it any more clear, Mr. President. We look forward to the day when we can end the Korean War. That will end - will happen when Kim verifiably gets rid of his weapons programs and his weapons."
If there were an ulterior motive for the South Korean's outburst, it may have been that he jumped the gun. Seeing an end to NoKo's threat, he would see no need for American troops stationed in SoKo since the technicality of a war would be over. If that's the case, we should not only remove our troops, but our submarines and ships as well giving them no more nuclear umbrella to sit under.