When sat inside of a boat, turning the camera doesn't turn the head of the character, they are always facing forwards.

As a result you can't look around to light up areas with a light source such as the head torch.
It's also pretty immersion breaking if you see other players sat in the boat as they feel like lifeless robots, always staring ahead.

https://www.youtube.com/watch?v=NmW_E2niXdA

This issue doesn't occur in cars, as is demonstrated at the beginning for comparison.