Why was the US ignorant of what was in Kim Jong-un's mind?

In all the pre-summit planning and discussion, how is it possible that the US team clearly didn't have any idea that Kim Jong-un was going to effectively scupper the meeting with Donald Trump by demanding an impossibe concession? He said he wanted every economic sanction lifted in return for the odd dismantling of nuclear installations. Did Kim really think Trump would cave in? Perhaps he did. That unexpected offer to cancel US/South Korean military exercises at the first summit must have made Kim hopeful of getting the president to make another gesture of a similar scale. But cancelling, temporarily, military exercises is wholly different from a total lifting of sanctions. Surely Kim knew that? But I guess he thought, "What the hell, if you don't ask, you don't get". But he took a giant step in the wrong direction, and Trump brought the summit to an abrupt end for which the president has received support even from leading Democrats. But in all the planning for the summit, did both sides not draw up a list of possible concessions? Was there any form of provisional agreement that such concessions would be presented to Trump and Kim for signature on Day Two of the summit? This is how summits work. Most of the hard labour is done beforehand and all the two leaders have to do is smile, be nice to each other for the cameras, crack a joke or two and get out the fountain pens. Months of hard work was thrown out of the window when Kim made a demand Trump couldn't accept. Now it's going to be impasse for months. Perhaps Trump and Kim need new negotiating teams. How about Kim's beloved sister on the North Korean side and Nikki Haley, ex UN ambassador, on the American side. I'm sure Boeing, her new employer, will let her go for a few months. The men failed. Let the women have a go!