Becasue the chances are so very small that this happened in this case. And now with LE charging JM with what they are, it diminishes the chances all the more. The evidence from the get go pointed to someone picking up or abducting Hannah, given that she was alone, lost, confused, and things went south from there so she was dumped off somewhere, hopefully alive, still alive, but maybe, probably not.
Hannah possibly went for a week long walk too and decided just to contemplate her navel, or many other Possibilities, but the case pointed strongly, strong probability that what happened was quite simple. The odds panned out on this. So we don't discuss the far fetched possibilities until the likely ones are eliminated, or we'd be looking for UFOs.
I don't think anyone cares if the possibility is brought up, that we keep an eye out for signs this might have happened, but there is the sentiment to give it about the same amount of attention to this as the probability of this happening is, which is small. Makes no sense to discuss it a lot. There may be forums that focus on this. Not this one