If you look closely at the Rubicon map, there is a room named "HR Layers of Reality." In the background, there is a pillar very similar to the one we see in Daemon during The Watcher DLC, but this pillar is cut in half (see image 1).
Let's remember that The Watcher takes place in a timeline where we ascend just like Saint with the difference being that Saint is trapped in a time loop, while The Watcher was able to break the cycle by becoming a void worm. It makes me think that this pillar represents your soul or your being within the cycle; there are infinite versions of you, but only one pillar.
The Watcher was able to work with the Weaver (a void entity) and ascend, but Saint is different. I believe the fact that his pillar is cut in half is a kind of punishment imposed by the void for trying to cross the limits of ascension and wanting to return to the cycle after having ascended. That would mean... the reason Saint is trapped in a loop is because he isn't actually alive... his soul was cut. There are no other versions of Saint because he no longer exists as such; everything is fake, just a dream.
This theory makes sense within the canon for several reasons:
1- Moon and Five Pebbles at the end of Saint’s campaign, suggest that everything is a dream.
Moon: "Little saint. I perceive your existence as it passes through my own. I know this is only a dream, but your presence is real. Where does your cycle go, little creature? Its edges twist over themselves, like circles within circles, your cycle consumes itself. What have you become?"
5P: "None of this is real, is it? Every repeating cycle of our own existence unwound and laid bare, a cycle pulled into a tangent with itself. Is this what we were looking for? Have we broken free from it, or is it just a dream?"
2- We know that Saint is trapped in a time loop and cannot escape, but if Saint knows this, why does he keep ascending over and over again knowing that everything repeats and nothing changes? maybe he doesn't know this, but that also reinforces the theory that the loop is a punishment and not something Saint chooses voluntarily.
3- The pillar balancing the spheres around at the end of The Watcher functions as a visual indicator that the protagonist has detached from all earthly ties and has been able to ascend, being considered worthy of becoming a void entity (or at least that’s how I interpret it). This means that the pillar is indeed important and functions as a connection between your soul, the cycles and the void, which is why we see hundreds of these pillars at the end.
(We can also see that one of the pearls contains an image of a hand trying to reach a white square. Maybe the Ancients already knew about the pillars and their connection with the void.)