There are more situations than just "a 55mph head-on crash" that need to be considered. What about getting clipped at 5mph when the driver is turning, and on a Cybertruck you've now got a brutal gash dug into you. And a camera that covers a full 360 isn't really all that useful when you're making a normal turn and not looking at the camera, but have your normal vision heavily obscured by the massive frame.

It's not perfectly safe. If it were, it would be legal everywhere and it's not.