International isolation
North Korea has garnered a reputation for being the most secretive country in the world. It has, of its own volition, become increasingly isolated from other countries ever since the end of the Korean War in 1953, which had started when North Korea – backed by the Soviet Union and China – invaded South Korea, which was defended by the UN (spearheaded by US forces). This level of secrecy is a key reason why the country creates so much intrigue, and suspicion, throughout much of the Western world. The country is subject to numerous sanctions and restrictions on trade and international travel, which further limits the options available to North Korean citizens seeking to leave the country.
Additionally, the government of North Korea has a history of using the repatriation of defectors as a bargaining chip in negotiations with other countries. This tactic has made it difficult for some countries to offer asylum to North Korean defectors, as they risk diplomatic backlash from North Korea.
Furthermore, the international community has limited influence over North Korea and its government's actions. This limited influence makes it difficult for the international community to provide assistance to North Korean citizens seeking to escape the country.