Something that occurred to me: the NPC that gives you entry items for Delve, the Anomaly Expert, has a mannequin head. Was that ever explained?
It's basically an other world entity controlling a mannequin to deal with you.
The HTBF NPCs are the same. All mannequins.
It's tangentially related to the simulacra that you have the old man snap together for Skirmish access. If you notice, they're grey statues/mannequins.
I'm guessing there was some sort of idea that didn't get fully fleshed out about giving bodies, essentially, over to entities from Tartarus.
All in all, though, it's just one of those unsettling details so there's no need to explain how an Adoulinian citizen that lorewise is too afraid to go into the jungle for the last five decades / too old could still know precisely what Delve is and how to access it, since it's like a dimensional fissure involving yet more Naakuals (which are monsters from Tartarus).