He was rewarded so quickly by the current administration, he thought he would have to concede nothing. He also thought the current administration was sumpremely more hungry to make any deal than he was; also reinforcing his belief he had to concede nothing. So he has conceded nothing, and he is not going to condede anything other than some fig leafs.
If the current administration realizes they misjudged Kim, they will concede nothing and Kim will increase when and how he behaves badly. If it is Kim that was right about the current administration, then look for a bad deal (like Obama’s with Iran) being made, just to say we got a deal.
I am not predicting which of the two scenarios will play out in 2020, but one of them will.
It goes without saying yours is the closest analysis on the forum as to what is likely going on. He held the high ground. Negotiation goes that way when one person at the table clearly wants a deal much more than the guy and gives away his BATNA.