I think if people had a post that they could collectively come to in order to offer up their clues in an easy, streamlined fashion, they would. They may be feeling like the rest of us, thinking their small clue isn't worthy of its own network post or not having the time to manage an entire network post based on a small clue or hoping that whoever had the rest of the clue saw their post and realized it related.

Maybe they're looking for an opening to share/exchange information more easily.

I think the issue with a NPC-ICly posting it is that none of the characters trust any of the NPCs like at all. However, if the post was just like a placeholder for all potential clue discussion and not from a specific NPC at all (even if the mod journal is the one that made the network post) then characters would use it more if that makes sense?