I can understand a lot of wars back before the formation of nation-states/feudalism having a lot of kin vs kin and the reason why it isn't really covered. These cadet branches kinda hated each other.
Later, after feudalism, we see the start of nation-states and I can imagine officers during the Austro-Prussian Wars/Wars of German Unification knowing each other. I can also see the Russian Revolution also have families split up. We don't hear this aspect of other Civil Wars, while it's played up during the American Civil War.
We all read how sad and how much the generals were when they realised they were fighting old friends. I assume that other Civil Wars must have their stories like this.
We don't hear this aspect of other Civil Wars
We do hear about this for other civil wars. A brief superficial basic-facts-only coverage might well not include it, but a more detailed treatment often will. For example, one can read about this in the English Civil War, and in the Thirty Years War. Notably, in the Thirty Years War, some families deliberately supported both sides, partly to make sure that they supported the winning side, partly to protect the loss of family lands to the Emperor (for supporting the other side), partly for ideological reasons, and partly for money or rank.
Moving to the 20th century, the Spanish Civil War and the Finnish Civil War were noted for brother vs brother (and one of the Finnish names used for the civil war is "veljessota", "brother's war"). Brother vs brother has appeared in popular culture for some civil wars, such as the Greek Civil War (the movie Deep Soul (2009) (Ψυχή Βαθιά)) and the almost-civil-war Korean War (Taegukgi: The Brotherhood of War (2004)), both of which feature brothers on both sides of the war.