This gives me impression like what happens to the nuclear weapon proliferation. At beginning, it is an arms race, between US and USSR, between users and advertisers. Either side thinks they can't survive without vanquishing the other. Eventually they realize it is stupid to continue, and reach a point to both step back. I think Mozilla is at the point where they realize it is no longer beneficial to continue the race…
Television and radio advertising exists and has existed long before the Internet without any need for detailed conversion tracking. Brief "To help us improve our business, could you please tell us how you heard about our brand?" questions in order forms has sufficed. A/B testing of billboard placements have sufficed.
Put simply, "Privacy Sandbox" is presented as a solution to a "problem" that doesn't exist.