Re: I wonder
What minuscule fraction of the billions of adverts launched actually result in a click through to the serving site; and what minuscule fraction of that results in a sale?
Unfortunately, that is the problem which is causing all this tracking. The reality, as I understand it, is that virtually no one clicks on an ad and buys the product in that transaction. So, Google promise advertisers that they can tell them when the ad contributes to a future sale! I can understand why advertisers who believe this would see this as a useful metric - likely to encourage them to spend more on that type of advertising.
That is what this Privacy Sandbox approach is promising to do: it tracks which ads were displayed to you, and it tracks what you bought, and it tells advertisers which ads resulted in a (later) sale. I have no idea whether it really does that very well - but that is what Google is promising advertisers.
At the same time, Google is trying to promise to us that it will not let advertisers know who we are and will not allow (for example) things like web sites adjusting prices because they know what we are looking for or what we have bought.
I have no idea whether what it is proposing can do either of those things. However, I am not willing to even let Google know any of this stuff (what about competitors to Google? do I have to tell them as well?). What I feel like doing today is none of anyone else's business.