If your standing is low, your fate would be subjected to the whims and manipulations of the more powerful. That was how the society of the demon worked. In essence, it still retained the primal form of law, the law of the jungle.
A gathering like the Hexennacht serves as a vivid reminder of this stark reality. Only the high-ranking demons here dominate the scene, a Demon Earl like Simon has no place.
Just like how right now he was forced to have the short end of the stick because the Demon Lord saw no worth in siding with a Demon Earl like him.
Of course, it was not like Belial did not put any consideration into his verdict. In fact, he had taken Oswell's standing into account because he didn't want his relation with the latter to break down, he gave that verdict. Or else, given Simon's standing, simply suffering from some concessions wouldn't be the end for him.
