It didn't?
Except once a joint exercise is performed, North Korea will be whiny, and correctly say the US broke the agreement. The US would have exhausted diplomatic capital for absolutely no reason or gain.
Will this ultimately improve things?
For North Korea, with lowered Chinese sanctions... umm... yes, a good deal. For the US, only for the idiots that think that meeting, in which:
- Trump saluted a North Korean general
- Trump praised how talented of a Dictator Kim was at such a young age
- Betrayed South Korea by unilaterally saying the US would postpone "wargames"
- Made decisions regarding our alliance with South Korea without even bringing it up with the Pentagon
- Signed a document he didn't understand (North Korea disarmament, what the US wants verses denuclearization of Korean Peninsula, what he signed)
...was a good idea.
Given that the situation couldn't get much worse, the risk is low and the payoff is high, even if the odds themselves are low.
The situation could get much worse, that'd be the nuclear war thing. The likelihood of nuclear war however seemed unlikely, though with Trump's bluster regarding fat Kim and fire and fury, people were curious whether Trump was actually dumb enough to try and pull it off, well, at least a conventional war.