I would posit that at least some of the problem is the lack of 'closing the loop' on the ad model. Even if Facebook does know everything about you, the ad buyer

I would posit that at least some of the problem is the lack of 'closing the loop' on the ad model. Even if Facebook does know everything about you, the ad buyers don't and instead bid naively using their best judgment. Whereas in an 'optimal' system Facebook should centrally[1] control who sees everything, dispensing the most valuable ad to any given user. In which scenario, because they control everything, they should be able to ML and optimize ads on a per person basis. [1]So that they can unambiguously determine ad end point value. Here they might even guarantee a sales per ad dollar spend figure - where they simply will not show the ad to anyone they deem less likely to buy the statistically profitable amount of product.