This is my theory about why the parents are dealing with the media the way they are:
I think they are only popping up in the media every few months because it allows them to claim that they are keeping the case alive, HOWEVER, when the case goes months without being mentioned by any media outlet; its appeal, public interest, notoriety, recognition, etc all drop. Back in October, it was the hot case so anything Deborah and Jeremy said would be analyzed by all media. But now, it's a cold case, and there are thousands of cold cases out there. Deborah and Jeremy can give one small interview, and they don't have to worry about it generating a huge media blitz with the entire country suspecting them again. Just look at the attention given to their 6-month-mark interviews; just local. I think the goal is to let the case be forgotten, but not be too obvious about it.