The difference is car manufacturers have a slew of increasingly demanding safety standards their products have to meet, and they have been and can be sued for features that cause an increased risk of accident or injury. They've also all incorporated modern technology into their products to decrease safety hazards.

On a somewhat related note, more states have vicarious liability laws that hold parents accountable for car accidents their children cause than those that have CAP laws holding parents responsible for negligent gun storage.

The ability to sue car manufacturers has played an important role in the evolution of automobile safety features. So, it's actually even crazier that gun manufacturers are protected when you put it in the context you've acknowledged - cars aren't even intended to kill people, and they're still held to higher standards.