This main question is what I asked myself many many times throughout watching this title. I really don't know. Even after finishing it, I still don't know the answer to it. The acting is really good, especially from the two main actors - the *prior to 2 days ago* popular SongSong couple. They are both very charismatic and do a good job. The story is interesting and unique. It plays at many different locations and never uses one for too long. Yet I somehow didn't get emotionally attached to this show as I would with many other shows. So why? I think the answer lies somewhere in the script writing and directing department. Even though the story is good and suspenseful and the actors are doing a good job "playing the story" they somehow fail to connect to the viewer on a deeper level. It's like they are playing the script for themselves and are playing emotional for themselves - not to appeal to the viewer aswell. It's a weird scenario I've never been in with a show, period. Not even on the american market.
Descendants of the Sun is a show with a very large potential but sub-par result at the end. Mainly due to just overdramatizing many scenes at the start and building up a "fake hype/drama" around the main couple. It was fine that the "I don't want you to leave me and how can I handle this" type of scenario was used once or twice, but they re-used it so much, that it actually got too obvious that it's just for the sake of drama. It kinda got unrealistic or unbelievable from the point of view of the viewer at that point. From that point on you would just not care about the effort the show would make to make it up to you as a viewer because you already were so frustrated that you couldn't care less. This is really sad in my opinion, because especially the main actors but also Kim Ji Won and Jin Goo did a wonderful job and it all got thrown overboard for the sake of an unrealistically high drama dose.
In the end, Descendants of the Sun re-uses this scenario once again and just makes you suffer one more time. So there isn't even an ending which would make up for this. There are slight glimmers of hope here and there, where you can feel happiness from watching this show, but it's really just for small things and not the two main couples, where the focus is mainly on and where it should have been done more right. I just can't give this show a 8/10 with the way it evolved.

More in-depth review: https://youtu.be/BgzK2_g82Rw