It's probably due to the Guardian's animation skeleton (Destiny)

by dogcow , Hiding from Bob, in the vent core., Friday, September 23, 2016, 12:46 (3076 days ago) @ ZackDark

Their heads follow the camera, up to a point. Bungie simply turned off head-tracking when looking behind you, but for some reason locked camera when the chin hits the chest/back of helmet hits back.

I wish they would have let the camera move past that point by a certain # or degrees. Sure my head stops going back at a certain point, but my eyes 'keep going' a bit more to allow me see right above me. I can see how the current state was arrived at with a 'proper implementation' (my ideal) as lower priority issue which just never rose to the top of someone's queue.

Anyway... Yes! Thank you for sharing the why in regards to the animation skeleton & camera, I hadn't thought of that as being the reason why the camera stops at that point.