I guess from the advertiser's perspective this standard could be a concern, because the loss of cookie-based tracking might make it harder for them to develop alternative attribution tracking methods that don't have the same data quality problems.
The mistake is assuming this replaces anything instead of becoming just one more piece of the tracking puzzle.
Even if it did "replace" cookies or whatever, it's strictly worse than "before" because it's giving advertising a front seat in the browser. My browser should be doing precisely nothing to help you attribute your ad impressions or whatever. But now Mozilla et al have to waste their time maintaining and augmenting this opaque piece of mathematical faff.
You don't need pervasive and invasive tracking and wholesale trading of your data to display advertising.
If not you aren't really working towards them paying a lot for ads, right?
Nobody "wants" ads, but they do want the free content they get today, which are funded by ads.
Why can't it?
No idea what it's replacing. Cookies is a red herring. Tracking involves more than just cookies.
It’s adding an additional feature that provides information to advertisers that they currently use cookies as one part of, with different considerations.