The context for this proposal is Apple has already been rolling out privacy protections for Safari and iOS, other players (like Big G) have had complaints, and this proposal undercuts those complaints. It's a negotiating tool, effectively.
Apple's privacy protections have made life harder for Google and other folks in the advertising space. Apple has basically tried to make it hard or impossible for anyone to stitch together user activity across different sites and build a profile of that user.
Advertisers have complained about losing ad attribution, and that complaint is legitimate. But, the existing techniques that are used to measure ad attribution also allow a excessive amount of additional data to be collected. Arguably, the ad attribution angle is just a PR-friendly fig leaf over what they're really worried about, which is user profiling.
So, Apple's counter-proposal: Here is a way to get ad attribution! Also, by the way, it doesn't allow user profiling, but that's ok, right? Of course it is. And now, ideally, we get to watch advertisers squirm as they try to come up with outlandish attribution scenarios that justify the collection of profiling data, while struggling to not admit what types of profiling they actually do and what fraction of their valuation that comprises.