The peace Agreement failed with North Korea because North Korean Soldiers didn't want to return to the North

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Armistice (July 1953 – November 1954)
The on-again, off-again armistice negotiations continued for two years,^[252] first at Kaesong, on the border between North and South Korea, and then at the neighbouring village of Panmunjom.^[253] A major, problematic negotiation point was prisoner of war (POW) repatriation.^[254] The PVA, KPA, and UN Command could not agree on a system of repatriation because many PVA and KPA soldiers refused to be repatriated back to the north,^[255] which was unacceptable to the Chinese and North Koreans.^[256] In the final armistice agreement, signed on 27 July 1953, a Neutral Nations Repatriation Commission, under the chairman Indian General K. S. Thimayya, was set up to handle the matter.^{[257]
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 It likely was embarrassing for North Korea that their own soldiers knew enough that there was no future for them in the North. So, likely they were forced to fight and when they found out how things really were beyond brainwashing, they knew enough not to return to the north because there was no future for them there at all. Only slow or quick deaths for having been captured as POWs in the first place in South Korea.}