If we are to believe advertisers are so great at their jobs, why can't they produce any meaningful metrics that don't commit egregious sins of statistical analysis?

Here's a thing that I am absolutely convinced happens. Ad network tracks purchases. Ad network track ad impressions. Ad network correlates the two and finds that 90% of people who saw the ad also bought the product. But they conveniently "forgot" to check if the ad impression was before or after the purchase.

I'm confident this is happening because the only times I see ads for anything I'd be interested in buying is after I've already bought the damn thing.