A lot of the surviving magicians who can still fight did not participate in the battle while some wanted to return to take some revenge or just to enhance their abilities against actual demons. Most just backed out due to the fear of losing their lives. Catmod and the others did not force them because it was really an unexpected event. The Phantasmal Reality was supposed to be the place where you can gain actual battle experience, not a place to experience the real terror of the demons.
The look of their faces has shown that most of them have experienced nasty things and I can say I can sympathize with them since during my time fighting against a demon, I almost got killed. But all I can tell is that I am no longer the same as them. I already managed to overcome my fear on them, its just a matter of experience.