[Same thing here. If NK is such an ominous threat, then why haven't the 2018 Winter Olympic Games in Pyeonchang, South Korea been cancelled?]
Because NK's intercontinental missile and nuclear programs represent strategic threats.  It seems you are confusing it with tactical level means of destruction.  NK has had the capability of targeting and hitting Pyeonchang (and Seoul for that matter) long before the Olympics committee decided to set the games there a few years ago.  In other words, the threat is not about a nascent or impending attack on North Korea but a shift in force projection and its affects on Asian geopolitics.
A nuclear NK will prompt a nuclear SK and likely a nuclear Japan.  Something neither the US and more emphatically China want.  Another worrying aspect is China's recent rise in international prestige is due to economic power.  It's diplomatic heritage is still developing so its ability to get things done with soft power, rather than hard power, is uncertain/weak.