There can be many factors here… one of which might be that I experienced Seoul.
People who live in Seoul (from my observation of myself and others) do not think of themselves as living in Seoul unless they are from elsewhere. People who have always lived in Seoul live in this or that part of Seoul, but they don’t live in Seoul. Everything happens in Seoul, whether that’s fair or true. And Seoul is Korea–again, regardless of whether that’s fair or true. (In fact, Korea is Korea, not North Korea and South Korea. Of course, in specific political contexts, people mention the North and South Koreas. But in everyday life, Korea is Korea.)
Seoul is always here and now. It doesn’t need to be mentioned.
I have never lived elsewhere where things are the way they are with Seoul. I have never even heard of places that feel like Seoul. If I had, my image of Seoul wouldn’t be what it is now.
Interestingly, as Ithaka, Seoul used to be the only named real-world city in my stories. (If I remember correctly.) In the cases of other place-names, I made things up.
Meanwhile, as Wynn, I am using more real-world place-names. But for longer works, I still don’t name the city itself where things happen. The idea of being able to look up the physical setting of my story on Google Maps annoys me. I don’t know why.
If there is one novel of mine where it’s accurate to leave the city unnamed, then it’s this WIP. Of everything I have ever written, this novel has the most real-world places named. It has the most real-world history-related elements named.
Yet the city is “the city.” It is always the city, eternal and fixed, only here, never elsewhere.