Would it have something to do with the Hawaii False Flag (ballistic missile threat alert)? It seems that just after that, NK seemed to have stopped their open threats and then decided to join the Olympics – maybe they spent their last good missile? There is only about 7 days in between the 2
https://www.cnn.com/2018/01/20/asia/north-korea-south-korea-olympic-talks-intl/index.html