That’s because personalized ads are hostile in the extreme and shouldn’t have been allowed in the first place. It pits millions of dollars of psychological manipulation against our “self control”.

I’d rather the economy burn than continue this unethical practice.

For that matter conversion metrics are not useful because the real high value purchase are not see ad buy thing. They are more of see many ads for SUV, when current car gets 'old' buy SUV. Many years of advertising are used in that targeting, and you cannot easily measure conversion.

Easily, no. But you can, at least in theory. With enough data, you can essentially tell if a customer has seen your ads, plus when and where (and not just your online ads - billboards and dealerships could be identified by using the customer's car to track their location). If they buy your car, and you see that they viewed your ads, maybe they even clicked one or otherwise browsed your site at some point, you can get some data from that. With enough aggregate data, you can begin to see correlations between certain ad viewing behavior and certain purchases.

Do they actually do this? Probably not, due to incompetence. But they could and eventually will if they aren't already.