South Korea's revolts show high risk and a poor chance of success. Two of the South Korean "anti-tyranny" movements succeeded, partly. The April 19 Movement of 1960 against the corrupt rule of Syngman Rhee forced his resignation, but any democratic benefits soon evaporated withy the military coup overthrowing the Second Republic, bringing in the long dictatorship of Park Chung-hee. The government's (i.e., Rhee's) first response was force: shoot the protestors. About 200 were killed, and many more wounded. The protests grew, and in the face of huge popular anger, the army and police refused to kill the thousands they would have needed to kill to try to suppress the protests. Rhee resigned the next day. Even beyond using illegal force to stay in power (e.g., arrest and torture and/or execution of political opponents), Rhee was overtly corrupt. He had failed to restore the economy after the war. He lacked broad support in the government and military. He was in his 80s, and perhaps prepared to retire.

The June Democracy Movement of 1987, the culmination of many years of pro-democracy activity finally forced President Chun Doo-hwan and the dictatorship's choice for the next president, Roh Tae-woo, to accept a new democratic constitution. Three major things contributed to this acceptance:

1. US pressure. While the US had been willing to accept the Gwangju Massacre, and help cover it up, they were not prepared to accept what would have been Gwangju-times-ten. Chun ordered the army into the streets, which would have quickly led to thousands of deaths. First, the US ambassador quickly conveyed that such use of force was not acceptable to the US government. Second, Reagan had a friendly chat, and convinced them to accept the inevitable.

2. Chun was not dictator-for-life, and Roh would not be either. After the wonderful experience of Rhee's government and Park "president-for-life" Chung-hee, there was a one-term limit as president. Even the dictatorship was not willing to accept past levels of abuse of power to maintain personal rule.

3. People who would have been first against the wall and shot in the event of violent overthrow would get to stay alive, and mostly stay out of the courts and prisons.

The democratic victory was not total. The dictatorship's candidate, Roh, won the democratic election, and the next presidential term was an uneasy compromise between military rule and true democracy. (Perhaps there would have been violence used for the former government to stay in power if Roh had not won the election.)

Other pro-democracy protest, and other anti-government protest did not far so well. The Jeju Uprising of 1948, protesting the division of Korea, was brutally suppressed, with tens of thousands killed, and tens of thousands fleeing Korea as refugees. The June 3 Resistance movement, a popular protest against the normalisation of Korean-Japanese relations, was suppressed with over a thousand arrests and hundreds of imprisonments. The pro-democracy Gwangju protests were also brutally suppressed (the Gwangju Massacre).

None of the elements that helped lead to the overthrow of the South Korean dictatorship in 1987 apply to North Korea. The leaders are not limited to a short term; they are leaders for life. US pressure is irrelevant. The leadership sees their best chance of survival as suppression of dissent rather than surrender.

North Korea is much more controlled than South Korea was. South Korea had active opposition and pro-democracy movements; North Korea has none (in North Korea; there are such movements in the defector/refugee community, with the North Korean People's Liberation Front as an extreme case). There is no significant opposition leadership in North Korea.

Protests such as the April 19 Movement and June Democracy Movement in the south would have met in the north, very quickly, the fates of Jeju and Gwangju. In the south, the violence ended in the April 19 Movement and June Democracy Movement due to police/army refusal to shoot the people in the first case, and US pressure in the second case. Neither of those protects North Korean protestors (nor did they protect the Jeju and Gwangju protestors in the south).

There have been protest movements in North Korea. One issue important to many has been the continuation of private trade (something the government has sought to ban in an excess of communist fervour). The government, at least de facto, gave in, and continued to allow private trade. The North Korean government is sensitive to popular anger, and pragmatically makes concessions. A mix of the prospect of brutal repression and sensible concessions by the government have so far kept peace.

Further reading:

Andrew David Jackson, "Why Has There Been No People’s Power Rebellion in North Korea?", European Journal of Korean Studies 18(1), 1-34 (2018).