As others mentioned here, the contemporaneous audience may be unaware of that era's lack of many conventions which are more or less assumed nowadays, including

As others mentioned here, the contemporaneous audience may be unaware of that era's lack of many conventions which are more or less assumed nowadays, including for conflicts/wars, so mentioning (unbiasedly) the brutality of a given interaction may paint a clearer picture, which is (or should be) the point of these articles. And as the time goes on and we distance ourselves from memorable conflicts, that may be increasingly more necessary if less and less of the audience would assume it by default. Regarding the difference in the level of war brutality that the involved parties experienced in history, one notable example comes to mind - mongols. I have yet to encounter someone willing to argue that the suffering that medieval mongols inflicted in their campaign was comparable to that of their opponents.