You're 100% right. I will never understand why ad spend is as high as it is when the customer never proves ROI. It made sense when ads were cultural background

You're 100% right. I will never understand why ad spend is as high as it is when the customer never proves ROI. It made sense when ads were cultural background noise, in magazines and other media that had no way of providing feedback on conversions, etc. But we've crossed the rubicon, and yet ad channels still suck at ROI for the perverse reasons that you correctly mention. At least some channels, like App Stores for example, offer something like end-to-end metrics for placements.