They aren’t nearly as safe as they could be, and manufacturers have had to be dragged kicking and screaming to implement even basic safety features like seatbelts: some manufacturers even refused on the basis that adding safety features implied their products were unsafe!
Airplanes are probably the example you want - heavily regulated and very focused on safety. Not motor vehicles. After all, if they really were focused on safety, they’d have banned giant trucks and SUVs for personal use a long, long time ago.
i think it holds up, but I get your point. Still, if 18-year-old me designed and built a new car in my parent's garage, I'm not going to be able to send it out into the world and make millions of copies of it for everyone in the world who wants one.
That's a pointed question as the infrastructure to support individual cars continues to eat the cities in the US and the climate continues to change from the CO2 released into the air, actually.
Had we known what the challenges would be, would we have made them so easy to own and operate? You need a license to fly a plane solo, and it takes years to get one.