Because many people need a car to function (get to work, shops, take kids to school). Nobody needs a gun to function.
I'm not sure that's a compelling argument. One could easily counter that people could move to be closer to work and/or school. Cars are "needed" because of the life choices people make.
> Nobody needs a gun to function.
If we apply consistent logic, there are people who need guns to function just as much as others need cars. Folks who live in the wilderness of Alaska and make a substantial living off the land need guns to hunt animals and acquire food. Sure they could hunt with a bow, but people could also get to work on bicycles.
What's the difference between an AR-15 "assault rifle" (whatever that means) and a hunting rifle used in Alaska?
Likely nothing. They probably have the exact same ammo, capabilities, and the differences are purely cosmetic.
There's also a lot of studies into car safety. Perhaps it would make sense to spend some money studying gun safety, as well?