Airport Screeners: Denied radiation badges?

From ScienceFriday:

I continue to wonder why those TSA folks who stand by x-ray machines for a whole day do not know how much radiation they are exposed to. Last weekend, one of them told me she asked for a common radiation badge and was told she could not wear one.

This weekend, when traveling through the airport at Buffalo, NY I happened upon one of those new whole body x-ray scanners. Refusing to be screened that way, I chose for a full body pat-down. Upon gathering up my stuff, I asked one of the screeners if she knew how much radiation she was exposed to each day. She said she did not know and wanted to wear one of the badges that her friend wears at a local hospital, but was told “no,” that would not be permitted. She was upset with that decision.

Why do dentists, doctors, med techs, etc.. who work in other x-ray environments gladly wear these exposure detectors on their clothing but TSA employees do not or cannot?