It is my belief that there are two primary reasons why Trump has agreed to meet with Kim Jong Un. I believe the timing worked out well for Trump, allowing him to use the announcement as a distraction from the latest round of chaos and malfeasance associated with both his own behavior and the troubles associated with those surrounding him.
Secondly, I think he finds the idea of meeting with Kim Jong Un rather attractive. Kim is one of the handful of world leaders that Trump truly admires and respects. Trump has always praised Putin, and recently expressed his approval for China’s removing term limits from President Xi. But Kim Jong Un is the autocrat’s autocrat. I have no doubt that Trump is jealous of Kim being to dispose of opponents by having them executed on a whim (by anti-aircraft gun, no less). Don’t you think he would have fired that gun at Jeff Sessions and Robert Mueller by now if he could? You know he would.
Anyway, the point is that Trump wants to hang with people who already have what he aspires to. Trump has to contend with the rule of law, he envies people like Kim who can say “My word is law.”