When the pathologically peaceful Schuul first began trading with humans it became clear that the two races were on the cusp of societal symbiosis. The Schuul, whose exclusively aquatic lifestyle precluded a number of high-energy manufacturing methods, needed industry. The humans, so crippled by their evolution that complex tool use was their strongest survival trait, needed room to breathe.
And so, in a deal brokered by the Gatekeepers, humans set up industry in assorted orbits of Celeschul's primary in exchange for living space in the unused, dirt-and-sky layer of Celeschul's biosphere.
The local name of the Schuul world, "Celeschul", meant "that which embraces the people". The fact that it happened to be homophonic with "celestial", a human word for "heavenly", helped human settlement along nicely. So did the fact that all the messiest industries were in orbit.
Celeschul became, at least ecologically, a paradise which embraced all people - except for the generations of people whose burrowed boroughs festered inside discarded container ships orbiting the great foundries in the sky.