1. Just spitballing, but perhaps he has recognized that it is a good and productive move for his country.
2. I don’t know why I should take a prepared statement by a South Korean minister as solid evidence for what is motivating Kim Jong Un. I don’t think they talk much.
It seems more likely to me that reported starvation and hardships inflicted by years of sanctions are taking their toll. That the DPRK’s elite are even starting to feel it now. Who knows though?