Should you never write a subplot if it doesn't enhance the main theme and conflict of the story? I have this subplot I am writing and it's there just to explain the political system of the country and why different factions kill each other using assassins. The side characters disappear at the beginning of the story and reappear later on during the final portion of the story. The main theme is how war can ravage one's soul, and the main conflict of the story is against a different country. Now, the problem is that the two side characters are literally robots and there's a lot of worldbuilding that went into this, so I can't really find a way to enhance the main theme from this subplot and can't really tie it to the main conflict of the story, because the war takes place in a backward and helpless country.
So the question is should you never write a subplot if it doesn't enhance the main theme and conflict of the story?