Case: seat belts. First introduced in 1949, three-point seat belt invented in 1955, Saab made them standard in all their cars in 1958, Volvo in 1959 after being shown studies with fatalities. The first compulsory seat belt law was in 1970 (Victoria, Australia), and only began in the US in the 1980's (with great opposition).
Case: ABS. Patented anti-locks in 1930-ish, the modern ABS in 1971, the system was slowly introduced first in high-end models, soon in every model. The US only mandates ABS in cars since 2012, Europe since 2004 (for new cars). Read: all cars were already being sold with ABS in those dates, except for the cheaper and shittiest ones.
Case: Airbags. I skip the history there, because airbags are still not mandated anywhere. They are subject to some regulations, but you can technically build and sell a car without a single airbag in it.
My conclusion: we should not wait or even hope mandates do anything. In the car market we should do our own research and trust (to a point) car brand safety records and voluntary tests like NCAP, IIHS or NHTSA. If a brand doesn't give a shit about safety unless under a government mandate, don't buy that brand, because they are decades behind safety standards.
Mandates are not the bare minimum in safety, they are well below that. Take for example one of the lowest scores in the current NCAP: Lancia Ypsilon 2015, two stars. Still, they have (not mandated): two front airbags, two side head airbag, belt pretensioner, belt load limiter, belt reminder and ESC. Fear no more, even if we find today that kids in the back raises the death rate in a collision by 20%, we won't see it mandated until 2080 if ever, way after car makers figure out a solution by themselves.
