The specific issue in the relevant wired article wasn't the policy and devices that are in use, but the abuse and mis-use of the policies and devices by TSA-hired agents. If the TSA is unable or doesn't choose to monitor and eliminate this behavior in its employees, but a private company does, then their could be a distinguishable, competitive advantage. In other words, allowing agents to request extra body scans of particular people they want to see (hopefully) isn't a policy mandated by the TSA that a private agency just can't avoid.

Which, although I hate the TSA, sort of makes sense from their perspective. What's the point of creating a consistent screening process if an airport can just opt out? The terrorists will just board at the airport with the weakest security. All of the security is then worthless.

Follow the money and if enough opt-out then all of those TSA jobs get "lost" and the TSA shrinks (so they go and do something else) and so the drive to keep this airport security theater pork around will decrease and might even kill it to put money on the next scare tactic response.