Consider it from, say, Japan's point of view. Before, when one of Kim's limp, sputtering rockets went flying over Honshu, PM Abe could race to microphone and denounce Kim in the strongest terms, and could count on pretty much everyone else doing the same. Now, when that happens, PM Abe knows that he will be criticizing someone who was just lauded by the President of the most powerful country on Earth, so he won't be able to rip Kim a new one as easily, let alone suggest a retaliation such as sanctions. To PM Abe, Kim is now less of a murderous rogue dictator who should be vilified, and more of a legitimate government who should be included in the world community and maybe even invited to organizations like SEATO and the UN, even though he just fired a nuclear missile over Honshu.
Because he's just been legitimized.