Yeah, the policy causes more cars to be sold, which is also an important thing to take into account.

But you initially said "If most people replace their cars every three years they’re not getting to 80,000 km before they buy a new one.", and that is plain wrong, the car is not scrapped after those 3 years, so when it changes owner for the first time is irrelevant. And that 80k km is worst case scenario, that assuming all electricity is generated in the least environmental way possible, in practice it's often <40k km that there is already a break even because not all electricity is generated by coal.