Why is it said that the president of South Korea is the most dangerous and difficult profession?

Among the previous presidents of South Korea, except for Kim Dae-jung, they all died well. Other presidents including Roh Hyun-moo, Kim Young-sam, Park Geun-hye, Lee Myung-bak, etc., all failed to die well after they stepped down. Therefore, the president of South Korea is a high-risk profession.

On the one hand, this reflects the immaturity of Korean politics and its serious control by the United States. On the other hand, the economy determines the superstructure, and the Korean economy is deformed and only controlled by a few large families.