It's not even really made clear how any of it works. Souls are presented as a 1-to-1 exchange earlier, presumably it takes a soul to make an Endless. But then we turn off the computer and they all dissipate, as if they are being perpetually sustained by souls over time. Which is it?

And it's probably too nitpicky to point out that some of them don't dissipate for sidequests, since that's probably more for the sake of game design rather than for the lore, but it makes it seem probable that they didn't have to dissipate or maybe they even chose to.