A year ago Kim Jong Un wanted two things: To develop a nuclear weapons program capable of hitting the USA, and direct talks with the US.
Trump said he would never allow NK to develop a nuclear weapons program capable of hitting the USA and that he would not engage in direct talks with NK.
Fast forward a year and who got what they wanted? Outside of calling Kim Jon Un names on twitter Trump literally did nothing to stop NK's nuclear program, and once they clearly had developed the capability to hit the USA with nukes he knuckled under and agreed to direct face to face talks just like Kim Jong Un wanted. That's the reason you haven't heard any inflamed rhetoric Kim Jong Un lately, because he won. He basically walked up to Trump and pulled his pants down in front of everybody. Now that he's got what he wants he can afford act all diplomatic and magnanimous. Dude's pretty happy. And it's a blueprint for what Iran will do if Trump pulls out of the deal with them.