You have asked for an explanation for a thing that "seems to you" while providing no reasoning that it is. The only difference between the two movements is forearm supination, which has essentially no effect on the lats -- look at their anatomy, pay attention to the insertion. Grip width is volitional, and that might have an effect on the lats during the chinup. If either variant is performed with a very wide grip, ROM is shortened. Rear delts can be weak shoulder extensors in the chin/pullup or strong incrementally-loaded whatever-you-call-the-motioners in the press, which I assume you are doing. And any trap work performed in the chin/pullup is completely insignificant when compared to that performed in the deadlift, which I also assume you are doing. The absence of the biceps is the only significant difference in the muscle mass utilization between the two movements. As discussed in the book.