u/OGSyedIsEverywhere

In the Japanese text, the uses of the term want, including in the Ancient Dragon's dialogue and Aldia's words at the end asking what you want when you walk away from the Throne of Want, are just the word desire. The Covetous Demon's name actually translates to Gluttonous Demon. And yet, the story is filled with examples of characters and places being twisted by their desires far in excess of anything the typical Buddhist notion of desire being negative depicts.

Shanalotte, Maughlin, Cale, Licia, Lucatiel, the Princess of Venn, The Covetous Demon, Queen Mytha, the Old Iron King, the Rotten, Vengarl, the Lion Warriors late of Forossa, the mutated hollows in the Shrine of Amana, the Graverobbers in Shulva, Elana, Raime, Aldia and Vendrick are all characters whose minds, bodies or actions are warped by their desires and Nashandra is the embodiment of desire itself, and half of these cases involve one of the many different kinds of hollowing, but the lore of DS2 fuses hollowing and curses in a way the other two games do not.

In DS1 and DS3 the Undead Curse is the side effect of the First Flame draining the humanity of the dark souls from humankind as fuel through a life draining siphon Gwyn implanted into all human anatomy as a part of some ancient treaty. In DS2 it is this, but it is also the case that physical objects can have a person's excess desire poured into them to draw it out of the person, creating an object filled with desire isolated from any conscious will.

In the case of Human Effigies and some Troches we see that this alleviates the First Flame's pull somehow and in the case of the Lion Clan's efforts to alleviate their symptoms through making curse jars and in the painting of Nashandra we see that the resulting objects have a contagious aura of the curse.

What was Tanimura, or his team, trying to say here? Why is the curse a tangible substance that can be moved around?

We don't know who built the evergaols or how old they are, but we do know from the variety of prisoners and their possible backstories that many different factions have the knowledge of how to operate them. Are there any candidates for evergaols that we can't rule out having been built somewhat recently, either in the early parts of the Shattering or in the age of plenty beforehand?