AMP was specifically opt-in and only websites with enough man power and interest to implement it did, if you wanted it you had to program an entirely different

AMP was specifically opt-in and only websites with enough man power and interest to implement it did, if you wanted it you had to program an entirely different page using Google's JS framework and restricted subset of HTML. FLoC is opt-out and requires zero intervention from web devs, if your website shows ads it's already part of FLoC, it can catch on if people do nothing about it.