DPRK has not been allowed to adjust, Santa. You cannot compare these cases because they do not experience the same conditions.
China was long ago brought into the western orbit, in the 1970s. China was effectively a US ally for the last two decades of the Cold War. DPRK has always had an American blockade on it. China has never felt the kind of military pressure that DPRK now faces. (Colin Powell threatened to turn DPRK into a "charcoal briquette") The US and RoK haven't even signed peace treaties with the DPRK. There are tens of thousands of troops along the DPRK border. In addition, as soon as the USSR collapsed, the Americans retargeted their nukes on DPRK, which is why DPRK decided to initiate a nuclear program of its own. DPRK quickly stopped its program when the Americans signed a bogus deal in which they would lie about providing light water nuclear reactors in exchange for an end to hostilities, normalized relations, and an end to sanctions - none of which happened. The US normalized relations with China in the 1970s. The US still has not normalized relations with the DPRK. The US stopped blocking Chinese UN membership in the 1970s. The DPRK wasn't allowed into the UN until the late 1980s. The DPRK's agricultural situation has always made it uniquely dependent on outside sources for materials needed for ag production. China has bountiful arable land and resources. Vietnam is the rice bowl of the world.
Nonetheless DPRK has reached out, trying to engage in trade relations with Japan, ROK and others. They have tried to set up SEZs, much like China. DPRK desperately wants to be a normalized country. It has pleaded over and over again for normal relations with America. Why would a hostile, intransigent country bent on confrontation make this a demand?
You just can't compare these situations. DPRK is more akin to Cuba, but even in that case not really because Cuba started out much richer to begin with, and there is no continuous threat of nuclear attack and armed invasion to Cuba.