I worked for a forensic engineering firm that did crash reconstruction. The crash recorders that record 3 seconds is generally enough. They are so good at recreating a crash just from physical evidence that a black box is just a bonus.
It is not that useful anyway, it only records driver actions, it doesn't record conditions outside the car like "was the pedestrian in the road or on the side of the road?" and "was that vehicle it hit sticking out in the road or was it behind the line?"