Trauma produces a variety of changes in the body including changes in production of various hormones. These changes in the nervous system result in a loss of homeostasis which in turn disrupts our natural information processing systems. That is why traumatic memories are not stored or experienced in the same way ‘normal’ memories are.
Further, because they are not processed in the usual fashion, it is more difficult to transfer those memories into more long term memories. Again, this is why traumatic memories feel like they are still occurring in the here-and-now because your brain has not been able to transfer them to the there-and-then.
All of this is to say, there are very understandable physiological processes that are going on in the brains of those who have experienced trauma. Those reactions are out of their control and so it is not their fault that they can’t just get over it.
So please have patience, either with yourself or with others who have experienced trauma. If it has been months since the trauma and there is no change in the emotional arousal or distress caused by thoughts of what happened it is time to call in the experts and get into therapy.