Quotes from the news wire:
I think (North Korea's) expectations were too high that the removal of Bolton would provide more flexibility on what the U.S. wants as initial steps, while certainly it removes some pressure for an all or nothing deal, it seems the gap between what the two sides want as a baseline and are willing to reciprocate still has not narrowed.
If the U.S. was really serious about negotiations they would have learned already that this wasn't an approach they could take. it's already been rejected more than once, and to keep bringing it up ... would be rather insulting. It's a non-starter and reflects absolutely no learning curve in the process.