Earlier quoted context omitted.
Footage existing and footage being released to the public are two different things. I understand there is a public Voyeur interest in seeing crashes, but how does releasing footage of accidents aid investigation or safety outcomes?
Considering how much effort it takes the NTSB to reconstruct the chain of events from the crash site and flight data recorder, any high-resolution video could be very valuable. In particular I think all airliners should have 4K "dashcams" considering how inexpensive the technology now is. Crashes aside, a high-res Tower view would also make a great live webcam for enthusiasts to watch while listening to LiveATC.
Far more useful would be an interior cockpit view showing the crew and the actions they were taking but a lot of that is recorded to the FDR on newer planes too.