Seoul is very close to North Korea. Indeed, during the war, the city was even at times controlled by North Korean forces. During this time, Busan was the capital of South Korea.
However, today, Seoul is by far the biggest city in South Korea, with 10 million inhabitants (compared to 3 million in Busan), the capital, the political and economical center of the country.
Why? Why have the South Koreans decided, since the war, to return to Seoul and make it the center of their country, when it is so close to North Korea, and currently within mortar range? Indeed, if war ever broke out with North Korea, experts estimate that North Korea could wipe out Seoul.
Obviously you cannot just pack your bags now and move down south to Busan, but, during the 50s, wasn't that the obvious thing to do? Why would you willingly move your civilians close to the border within close range of the enemy? Even if North Korea didn't have this heavy artillery back then (I am pretty sure they did?), surely it should've been obvious that at one point, they would have such artillery, so Seoul's location is not optimal and Busan should've remained the capital?