Maybe, or maybe the FBI were just incompetent in this particular case and at that time didn't consider it prosecutable.

>Edmondson told the Times Union the FBI agent found the brandings disturbing, but said he did not see anything illegal about it — and said it “seemed like it was consensual.”

One could argue that Scientology similarly blackmails its members and compels them to make humiliating acts of submission and servitude, but one could also argue that it's consensual and not necessarily illegal. That was probably something like the FBI agent's thought process.