So, Foxfire would say "there's a reason he's gone undetected this long...".
What is this reason(s)?
ETA: Answering myself: Skilled, experienced hunter.
My reasons:
0) LE has not released enough information for potential tips to be made. The secrets LE are keeping are hindering their ability to identify the perpetrator(s) via public assistance.
1) Perpetrator(s) not from the area, more than 50 miles away
2) While BG looks like someone they know, the voice is totally different
3) While the voice sounds like someone they know, that person does not look like BG
4) No one who knows BG and/or the voice believes that person is capable of committing this crime
5) Not an RSO
6) No felony record
7) Perpetrator(s) understands investigative techniques, especially tracking of phones, vehicles that have OnStar (or the equivalent) regardless of whether subscribed or not or rental vehicles that are tracked by GPS, etc.
8) LE has not located the murder scene, thus they can't use that location information to learn more about the perpetrator(s)
9) LE does not have Libby's phone, thus they can't learn anything more than what they had the morning the girls were found.
10) LE has only in passing said it could be more than one involved, thus any witness that might have seen two or more people that were "out of place" hasn't tipped that because they are under the impression LE is looking for only one person - BG.
My main concern is that there were potentially very useful tips out there that have never been called in because the tipsters have not been given the information necessary by LE to make that tip and releasing any information later could very easily result in no tip being made because the person that could have made that tip has forgotten, now mis-remembers, or is no longer paying attention to this case. Some of them might have seen the witch hunts and that deters them.
LE has done themselves no favors by withholding the most basic pieces of information that in no way whatsoever would compromise their case. We don't have a timeline. We don't have a height of BG. We don't know where the girls were dropped off. Simple things. As I have said before LE doesn't need to keep hundreds of secrets to preserve the integrity of their case.
Another concern is that LE has been trying to bluff the perpetrator(s) into thinking LE knows more than they actually do. This has evidently not flushed out a suspect, if that is the case, and that would mean BG has absolutely no concern whatsoever that LE is going to be knocking on their door, let alone even speak with them or let alone ever arrest them.