Is there an option to turn this on? Am i missing something?
Looks like Horizon again is lacking a rear view mirror. That was my biggest frustration in the original Horizon. 
Nope, no option. The only rear view mirror you get is in cockpit mode. You can always try to hold the right analog striaght back to look back - or use the replace camera with look back option.
Ugh why… Debbie downer, no rear view mirror in hood view.
Considering what the in-car one looked like in the original Horizon I understood why they didn’t show it in hood view, but I have no idea why the option wouldn’t be there in the new one.