But not if the fixed regulatory overhead is equal to the margin on twenty thousand cars.
"Individuals have built cars out of parts in their own garage" doesn't really prove that the costs for producing a car isn't high. They're most certainly enthusiasts, and they could have plowed tens or hundreds of thousands of dollars worth of parts/labor into it.
On the face of it I'm with you, but then when it came down to it I'd be thinking well hang on this actually doesn't seem as safe (or at least not as thoroughly tested to determine if it is) as these other mass-produced things, and wouldn't end up buying it.
If it was easy to make something as safe as a $modern_run_of_the_mill_family_car and that looked 'normal' (i.e. curvy, I suppose, not weird slabs of barely bent sheet metal) I think there'd be loads of Kickstarter campaigns 'basic'/'maintainable'/.. cars.
It's possible and even likely that we have rules which are unnecessary or not worth the cost for small production runs, but which apply to them anyway, because companies doing small production runs don't have lobbying clout and companies doing large production runs are amortizing the cost over hundreds of thousands of cars and don't want things to be easier for smaller competitors.
