A Justin Barron going on waivers isn't a future star or a young RD, he'd be a fringe NHLer. At that point, his value would tend towards 0, and unless a team has space due injury, he wouldn't be claimed. Rebuilding teams have their own fringe NHLers also. One more, just to throw dices in the place of one of your own is not good management.
Incidentally, that might be why he wouldn't be waived. Just to protect his value and see if any teams eventually in need of him can give something for his services, like a certain Ylonen. See where that lead him though...
They were waiting to get something for Allen at the TDL and he was on his way out, not Primeau. It's not the same context if Barron doesn't cut it. There isn't anyone who's going to make room for him, if he's not a NHL caliber dman.