backup cameras are nice, but are marginal at best as safety features even though they're marketed heavily that way. they're for convenience, so we don't have to crane our necks when backing up or parking. seat belts, on the other hand, have easily saved thousands of lives.
point being, mandating backup cameras is an overreach of safety regulation, but not for seat belts.
The individual who lead the effort to mandate backup cameras (after backing over and killing his son) cited ~200 deaths and 15,000 injuries, annually, mostly small children and elderly [1]. I don't know if I'd call it overreach, but I also don't know what the equation is for cost versus tragedy when looking at an issue like this.
running over anyone is tragic, and i'm not trying to make light of it, but that's the same misapplication of risk, fear, and bias that lead to security theater, housing crises and regulatory capture generally.
we don't regulate for the people (US, annually) who accidentally drown in a bathtub (~300) and get injured in a bathroom (~250k), even though it would address more harms (at a larger scale and possibly greater cost, depending on the mitigations).
Backup cameras cover a blind spot behind the car that’s large enough for a child to not be seen if you’re craning your neck the old-fashioned way. Obviously they aren’t as important as seatbelts, but the biggest improvements to a new invention tend to be the ones invented earlier anyway.
The next big safety feature will be one which lowers windows in the presence of an occupant in the rear area if an occupant has not been observed in the drivers seat for x minutes if the temp is above 60F/16C for example.
While it would be obviously a good idea it will not be do-able from a technological point... first, because such a detection, most likely with cameras, would need to always run even when the car is powered off. That means a lot of electricity being wasted. Second, because it will get abused by thieves - projecting, e.g. with a laser, something onto the cameras and boom, the windows open.
point being, mandating backup cameras is an overreach of safety regulation, but not for seat belts.