Or perhaps they are scouring the universe for all places like Earwa where the Outside can be reached, and are slowing colonizing the closed worlds behind their Inchoroi armadas.
This.
My guess was about other planets of Bakkerverse can form topoi or be subject to anti-topoi measures (which is technically approaching to the Outside / distancing from the Outside, opening the World / shutting the World). But they have no sorcery. You will have to shut these world manually one by one and hope one day you will find or research some new, more efficient, universe-wide method. Inchoroi were lucky to find sorcery, gnosis and Shaeönanra, lol.
Assumption is. Sorcery is an "intelligence within intelligence", a rule-breaker. There is mostly empty space in the universe. Sometime there are stars. Even less, there are planets. Life is ever more rare thing. Intelligence? Much more rare. Intelligence capable of sorcery? Maybe the rarest thing possible.
Without sorcery you can create topos-wide planet by torturing it's intelligent population. Without sorcery you can shut the said world through forced evolution (torture is about pain, pain is about experience of tissue trauma, science can destroy the very existence of torure, including psychical one -- nonmen innoculation seems like a botched attempt of it).
But it's just a local event. After making the numerous population, ahem, into 144000 post-specie creatures, you are safe on the shut world. Gods won't recognize it or you anymore. It's better than to just count on your immortality and never dying, but it's still a procrastination. Contitents will migrate, supervulcanos will awaken, stars will grow and devour a whole planet. One day you will have to pack your tekne and find youself a new world, starting the cycle again.
With sorcery you can completely change the field and the rules of this game. So to say, you can gouge out eyes of gods instead of acting stealthy in front of them. Go full assault instead of hiding.
TL;DR Earwa is a final, non-procrastination solution to the Outside problem.