With a finalized class settlement, Google would have stopped fighting for fair-use rights, and entered into a moneymaking partnership with the Authors' Guild with a unique right – established by the expansive class including all authors not yet even identified – to scan and even market books, and be immune from further lawsuits from the class.
Anyone with shallower-pockets that then tried to do what Google did would likely have been sued by Authors' Guild – now strengthened by Google cash – or other members of the class. There was no precedent or requirement that others be offered the same deal as Google: if Authors' Guild liked their deal with Google (and why wouldn't they), they could tell others, sorry, we've already got a system in place, you're not part of it.
But further, why should other 'little guys' have had to fight a legal battle with Authors' Guild, or negotiate under threat of litigation by a de facto Authors' Guild-Google alliance, just to do something that (now, finally) is clearly authorized by fair-use?
The class settlement's Google-financed-and-managed system, for the benefit of the Authors' Guild class, would have started with an overwhelming and likely legally and economically insurmountable advantage in the scanning and marketing of older books. That gave rise to the centralization and privacy/censorship concerns of the ACLU, EFF, and American Libraries Association. They're smart and like old books, too – but perceived a risk that outweighed the benefit of "just scan 'em all quickly – under a Google/Authors' Guild monopoly".