Doctors make very good money on "fee for service" and will fight tooth and nail to block payment for performance, under which a doctor would not necessarily be paid a fee for service, and possibly receive a penalty for service.
One result of the ACA's implementation is that it has accelerated the trend of physicians becoming direct employees of hospitals and health systems. Thus many providers are at least temporarily isolated from income disruption due to changes brought about by the ACA. Of course soon as payment for performance and fee bundling reductions starts hitting the hospitals in earnest, then and only then will the physicians be subject to lower compensation and start to make a fuss.