Maybe it's because folks assume traumatic events are something the person can't help but constantly think about.
But for me, and I'm guessing most others, you tend to simply block off that part of your psyche. For example, I have forgotten my sister during introductions in the past, despite the fact she didn't leave my life until I was eleven. And I suppose she didn't really exit my life then either, she would continue to show up over my teenage years as well. But it's like my mind wrote her out of existence.
Also, when I write about the events of my past, I tend write them from a perspective that is dissociated. It's hard to explain. But I think it's a way of protecting myself. Like pretending the events happened to someone else.