It is up to the consumer whether it would be better to spend their limited budget on upgrading an older car where safety retrofitting is not possible, or on mig

It is up to the consumer whether it would be better to spend their limited budget on upgrading an older car where safety retrofitting is not possible, or on migrating to a newer car. You can't have a standard for a technology that doesn't exist yet. But anything that does have a standard can likely be repaired and upgraded more cheaply in the future. It preserves more of the value in the used cars. If someone really needs those side-curtain air bags, they would be able to trade in their old vehicle, at a higher price, to someone who doesn't value safety features as highly, and use the proceeds to help pay for a newer vehicle with more of those features.