See, you have it backwards. It's exactly the opposite. FLoC etc were designed to mitigate the antitrust concerns by replacing 3rd party cookie tracking for the other ad companies, allowing 3rd party cookie deprecation to proceed. By blocking FLoC, activists made it impossible for Google to deprecate 3rd party cookies in Chrome, as that would guarantee a loss in antitrust court.

Google themselves never needed FLoC for their own ads business. Their search and video ad businesses don't need 3rd party tracking to be successful. Google has the most first party data; users literally tell Google their intent directly by typing it into the search box. Advertising on 3rd party sites is a small minority of Google's revenue, and the part of that attributable to cross site tracking is even smaller.

But Google had to provide something to replace cookie tracking for the other ad companies that don't have the first party data Google has. Those ad companies rely on 3rd party cookies to compete with Google. If Google blocked 3rd party cookies in Chrome with no replacement they would instantly be sued for leveraging their browser market share to kill their competition in the ads market, and they would lose big.