I know that in the rule book it specifically states that cameras can't be used as substitutes, but why is this? Was that rule made back when cameras were really expensive and thus gave an unfair advantage? Do they get covered easily by debris? How come Kirk Swaney's vehicle, which has the record on the back of the hand book, was able to use cameras in place of mirrors without being disqualified?
I believe its the idea that cameras can run out of battery, or malfunction, while as long as your mirrors are attached properly ( this should be checked in tech ) has less possibility of failure, also you have to consider how your are going to display ( output ) the video, the easiest solution would be to have it display on your phone or a screen inside the car, which would take your eyes off the track to look down, not to mention if you put the screen inside the car, with the limited space you probably cant put anything that big, and it would be difficult to see what would be in the video with a small screen.
Kirk's car normally has mirrors when he actually races it. When he ran in the world of speed at Bonniville Salt flats we allowed him to take his mirrors off since he was not racing anyone and did not need to see behind him.
Mirrors are required as apposed to cameras for all of the reasons posted above.