To be entirely fair, the current South Korean government is called the Sixth Republic of Korea. The First Republic began in 1948 and ever since then, there has been a total of five instances in which the government had been completely uprooted and replaced with a new one, until now we have the current Sixth Republic.
Ever since 1948, North Korea has only had one government (i.e. the Democratic People’s Republic of Korea).
It could be argued that maybe North Korea is bad for different reasons, but lack of stability definitely isn’t one of them.