In the canon Star Wars comic, Obi-Wan & Anakin, the Jedi pair travel to the planet Carnelion IV, where a distress signal has been sounded. The planet is ravaged by war, with its most advanced technology being a walking tank or something. The people use bullets and airships. All I want to know is why. Have Charles Soule or some member of the Lucasfilm Story Group said anything regarding this and its story purpose?
In an interview on StarWars.com, the writer Charles Soule explained his approach towards the story. It does not give a direct answer to the question, but helps out in reasoning the background.
"They're going to meet up with a diplomatic fleet and then they hear a distress call from a planet that's supposed to be completely dead, there's not supposed to be anything on it. So, they answer the distress call and that's where the adventure begins."
Like Obi-Wan told Anakin in the beginning of the story, the people of Carnelion IV destroyed themselves in a war generations ago. The genocide and hypothetical destruction of hi-tech blasters and vessels at same time justifies the existence of the backwater world. Firearms and airships seem to be a visualization of that to us readers.
Also, in order to keep the planet isolated and the destinies of its people unknown, they must not have anything hi-tech for interstellar communication or travel in large scale.
"That's how I broke into it, and then from there, it was fleshing out a world and a planet that hopefully would seem fresh, that we hadn't seen before, and a type of Star Wars story that we hadn't seen before."
Soule wanted to create a unique world and probably thought a low-tech world would be more of the kind. Of course, there has been such planets in Star Wars media before, but they're still the minority.
"The series is set on a planet with mountain peaks over this huge rolling sea of green mist that obscures everything below because it's a planet full of secrets. It gives you some opportunity to do some really cool visuals with Jedi hopping around, using their lightsabers in the snow, stuff like that."
The comic book creators were after good-looking visuals. In order to justify such vessels as the Zeppelin-type airships, they thought they needed a low-tech world. And the airships did look pretty cool.
You can read the full interview here.