These are some ideas/speculation I had while listening to the series on audiobook. I will try my best however my English isn't perfect. I will probably edit this post a few times if people like it.
So, let's start with the metaphysics of this universe. My idea is, that in this world consciousness exists outside of the body. You would call that a soul. So, you need a physical body capable of "tuning in" ( a brain) a medium (space time itself) and a destination( a "soup"of souls). These souls basically exist in a dimension we can't really see. When a person is born, his brain attracts a soul,depending on what he is(and luck) he will get a particular soul.After you die your soul goes back and adds energy to the "pot". Superficial things about yourself are discarded and get mixed in with others(memories etc). "you" however survive, the reason for it is simple, you have been tainted by the "outside outside"(aka the real universe). Knowing what it means to exist your soul wants to exist, it can no longer not be.
Like in our universe, some places are more dense than others.The Inchoroi found out about their own damnation with the inverse fire. In there world this force was very weak, it existed(like everywhere) but it didn't manifest itself as magic. Using complicated technologies they where able to look into the "other side". Fire burn stuff, inverse fire burns INTO stuff, in this case, they could burned away the barriers and studied the outside, even if just superficially.
They realized where consciousness comes from, and they realized there's no way to actually escape it. When you die, your soul gets transported there. There is no technology in existence to stop it,even immortality will fail one day. And of course, the more you live,the more you are as a person and the more you will suffer.
They came up with an insane idea. Find a new home for their species. Knowing what damnation means,they where desperate enough to do anything. The idea was to send in seed ships and call in others for help/when it's done. However on Earwa most died in the landing ( and maybe the ship was damaged, they couldn't send a signal)
Why Earwa? Paradoxically, because the barriers between the real and outside are weak. In the rest of the universe, if you would try to change something it would be like fighting against the laws of physics, no matter how advanced you are, the universe fights back. On Earwa it is possible. Even if the boundaries are thin, you could use that same principle to keep everything out. Think of it like a transaction,everywhere in the universe the outside exchanges energy with the real. On Earwa you get a lot more, but because you get more, the barriers are weakened. All you need to do is keep the population low. If it's low enough, the souls being born will stay here. You will create something like the greenhouse effect for souls.
Paradoxically, the souls are the ones keeping the gate open, because they are constantly going back and forth. IF you would reduce the population drastically Souls would enter but not leave, because the energy required to leave would be to much, it's too much "pressure in the tubes"
Lets say,that the inchoroi somehow manage to close the outside. This would totally destroy them. Remember, intelect/the soul is linked to the outside. If they somehow would create a haven where nothing comes in and nothing goes out, they would practically kill themselves,and when the technologies fail, the soul would just go back to suffering.
That's why Earwa is the only place a shutdown actually works.It has everything in it's favor! The barrier is weak enough that souls could get in and the at the same time you can manipulate the laws of physics in your favor.
