There has to be some sort of incentive either for smaller cars or against larger cars. Currently you can go into a dealer, tell them you want the biggest baddest truck/SUV that they have, and buy it all while having a normal license.
You’d only be paying a slight premium on whatever road or fuel tax if that while having the benefit of not getting destroyed in a car accident. As it stands, there is little reason to buy a larger vehicle unless you actually don’t like driving a car that big.