Setting minimum standards is a critical function of governments in maintaining healthy markets because it prevents cheating from being cost effective. If you make a safety feature optional, you will have some fraction of people say that they don’t need it and then cost society money when it turns out they were wrong. In the case of poor locks, even if much of the cost is paid by the owners’ insurance there’s still a lot of expense from the extra police and court costs, and stolen cars are often used to support other crimes.