Most people who buy new cars do so when trading in their old one.
Imagine if people couldn't trade in their old car and had to keep it forever or have it scrapped/recycled?
Or, imagine that if they sold the car, half the features on the car stopped working.. say, because the radio required a non-transferable licence key which expired when sold, so requiring the new owner to buy their own.
Depreciation of used cars would be even worse than it is now, and the reduced sale price of used cars would fall and people would be hold onto them longer. New car sales would also fall significantly in response, and either manufacturers or dealers would reduce their prices to try and boost sales, or simply that there would be a big shake-down and manufacturers and dealers would go out of business to allow the survivors to maintain volume and margins.
In the meantime, "piracy" would increase as people found work-arounds to renable or retrofit features to their cars to add and restore features "stolen" by official dealer network. There would be a boost in jobs for people to repair or maintain older cars, and cost of spares would rise, and thus growth in third party components, and a backlash from manufacturers trying to copyright, patent or trademark spares to prevent that loss of revenue to unauthorised parts manufacturers.