> half of their ad spend was "wasted"

That would be a phenomenal ROI. In almost all advertising contexts the hit rate is far, far lower. Resulting in everyone drowning in ads to hit the few targets.

To the commenters saying, "but how will people/companies know what to buy?"... 1) Through the same high-quality information channels you usually use today: customer reviews, word of mouth, point of sale, and lived experience. For B2B, you could still have industry events or demos where it is essentially a physical opt-in for advertising. 2) I could not possibly care. The offsetting benefit of living in a world where I am not surrounded by messages trying to deceive me into spending money is well worth losing whatever tiny signal might be in that noise.