It was the same with opting out of the backscatter scanners when they started rolling them out. They had signs up saying you could opt out and instead receive an "enhanced" pat down, but TSA would make a big deal about it. They'd shout "We have an opt out!", pull you aside, and you'd have to wait for someone to be available to pat you down (which was itself an unpleasant experience). The vast majority of people don't want to go through that and just accept the scanner.

These days I don't even know if it's still possible to opt out. I haven't seen a sign saying you can in ages.