ouhh watched a video of someone playing saint for the first time and im having some saint thoughts. i think the most canonical way to interpret their campaign and behaviour is as follows:
the world is being devoured by the void sea. that's why rubicon is there now when it never was before, and that's why it incorporates parts of the real world as they were in the past (even pre-collapse five pebbles). this was all bound to happen inevitably, as per the subterranean echo's words to saint; they just happened to have the unfortunate fate of existing at the same time as the world finally started to be fully devoured. there are no more working iterators, and the ecosystem partially falls apart in their absence, but we can also see it surviving and the creatures adapting (lizards growing crests, slugcats becoming fluffy) to match. things will keep living even as the void sea devours the world, because that's simply the way of life in rain world: you keep living. everything keeps living, everything wakes up again, whether that's in day to day "respawning" or in reincarnation after actual death. and in a way, this is reflected by saint's failure to ascend-- perhaps by all slugcats' failure to ascend, if we look at the ending cutscene as them swimming towards an "egg" to be reborn anew. you can end one life, sure, but you'll always wake up in the next, in the same way the world ends only to begin anew (subterranean echo, undergrowth echo). but their failure to ascend, except in the case of saint, is framed as something beautiful! they are returning to their kind, they are waking up into the world once again as something new. that says a lot about how rain world as a media views all this i think. it's not about letting go and leaving life behind; it's about moving on, and finding new beauty in what remains.
i also think saint failed to ascend, as others have said on here before, because of their urge to ascend. that's what made the other echoes, echoes, after all. perhaps saint's campaign is just the memory of this echo being forever relived as it sleeps, waiting for some sentient creature to track it down so it may give a monologue and grant some karma. and in that vein, i don't see the other slugcats' gaining of karma as them necessarily growing and letting go of worldly attachments to ascend-- i think perhaps the reason none of them except artificer (and we'll get to her in a minute) truly leave behind the cycle of reincarnation is because they all have some desire that's never truly snuffed out. for survivor and monk, it's to find their family; for hunter, it's to make their creator proud, or perhaps return to him. gourmand is thoroughly attached to life and its wonders; rivulet, arguably the same. spearmaster, like hunter, wants to return home to its creator and rest.
artificer, if she chooses to ascend, i think really does leave behind worldly attachments. they accept that their children are gone and no amount of revenge will bring them back; they still hurt from the loss, but she accepts and no longer tries to change it. more importantly, unlike in the normal ending, she renounces the violence that tied them so strongly to this world, and without that to fuel her, there's not much left of them, hollowed out by loss. they are truly granted peace when they ascend; they feel their children again, just for a moment, and that peace and solace that that moment brings is enough for the void sea to completely erase her. it's sad, but i almost think it's a better ending than the normal one (though of course gameplay wise the scav king is more fun).
saint is not like this. i don't know why they try to ascend the void worm-- maybe just to bring an end to their cycle, if they truly are trapped inside a loop and not just endlessly reliving their past as an echo, but either way, i don't think it's that that prevents them from ascending (at least not entirely). for the void worms to "curse" them and trap it in a loop implies more conscious action than i think those creatures have-- after all, this is Subway Rat Simulator The Game. at the end of the day, i think it's far more interesting for the void worms to just be creatures like any other, going about their lives, eating the world for no other reason than they're hungry and they need to live. no, i think the reason saint fails to ascend is because, in their last moments, their only thought is of ascension. unlike artificer, they still CARE so strongly about ascending that they even try to ascend the void worm, and it's that attachment to the idea of ascension that they're so unable to let go of that turns them into an echo, trapping them cruelly in the world they tried so hard to escape.
saint can't see the beauty in it. it can't see the point of living on, of finding beauty continuing to bloom in a place thought dead and forgotten. THAT is why it's trapped.