I think those entities need mortals, those with soul and free will to tie themselves to the material realm.
For some reason I could see some of peace talks carried out on demon reach due to its security.
Once an entity is forgotten, it might become vulnerable. It could loose what power it has and fade away, the energy draining into the well. At certain places, immortals can loose or gain energy, so if forgotten it might imply it can no longer retain power.
I have this theory, that the well can be used against those linked/tied to the inmates. Sort of how the rcv essence was stripped from mortals. Say all the skinwalkers were in the well, the well could be used to strike their descendants and apprentices, those that use their corrupted lore. The skinwalkers are kind of the source of their power. Sort of like how the faerie queens are tied to the courts, if one is affected so the other would as well.