Why is there so little talk throughout the story of the enemy?

Remarque's focus is not the enemy per se; the story is all about how dehumanizing and emotion killing war can be, so the focus is on the characters and the ways in which war changes them. In a universal context, the actual enemy matters little. The talk is about those who are alive, those who are dead, those who can remember the past, and those who cannot picture a future. The main characters die by the end of the novel; those who might live through the war are only the shell of the people who began the war. The enemy is, at some level, irrelevant.