Because as GP alluded to, the thing it's replacing (cookies) already does exactly the same thing but isn't anonymized.

> the thing it's replacing (cookies) already does exactly the same thing but isn't anonymized.

No idea what it's replacing. Cookies is a red herring. Tracking involves more than just cookies.

It’s not replacing cookies, though.

It’s adding an additional feature that provides information to advertisers that they currently use cookies as one part of, with different considerations.