in my limited experience: my understanding is that oral intubation with a scope usually requires atlanto-occipital extension, to bring the cords in sight. If you have C1 or C2 injury, you want to avoid this. Manual in-line stabilization can decrease this disruption of the c-spine.
blind nasotracheal intubation won't disrupt the C-spine, and therefore is preferred. you want to avoid nasotracheal intubation in midface or basilar skull fractures.
there's always orotracheal fiberoptic but in a trauma pt you may not have time (you mght be in the trauma bay, the pt is crashing)
so that's why nasal intubation with unstable neck injuries.