I'm more curious as to why there isn't constant video logging. Reports are that 80% of drivers consider themselves above average, and consequently the belief must be that accidents are caused by the other parties who must be below average. Add in driverless cars, and again the "above average" driver is going to know those are at fault.
While the black boxes help a bit, they don't show the corresponding actions of other cars, state of traffic lights, exactly what lane other vehicles were in, reaction times etc.
Video recording is the final piece of the forensic puzzle. The new cars and driverless cars are going to want it to show they are not at fault, the above average drivers need it for the same reason, so we are only left with a small minority who won't believe video is to their benefit.