Safety features in cars usually get invented before they become mandatory. Backup cameras took about a decade to become mandatory, too.
point being, mandating backup cameras is an overreach of safety regulation, but not for seat belts.
[1] https://www.kidsandcars.org/2018/05/14/after-his-sons-tragic...
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).