[quickthrowman]

Two reasons.

Artillery aimed at Seoul: https://atlasinstitute.org/seouls-48-hour-nightmare-from-nor...

Nuclear weapons that can hit Japan (and US bases in Japan): https://en.wikipedia.org/wiki/North_Korea_and_weapons_of_mas...

Plus, the quiet part that nobody ever says is neither China or South Korea actually wants to reintegrate a thoroughly brainwashed population. It would be the worst refugee crisis ever by at least an order of magnitude.

German reintegration was difficult enough, reintegrating Korea would be much harder

[rtkwe]

That's out of date, they can nominally reach the US mainland now with nuclear payloads. Accuracy and reliability are somewhat questionable but it's a huge gamble.

https://missilethreat.csis.org/missile/hwasong-17/