Well, a long time ago, Hell rejected them, accepting them would mean declaring war against all the gods. While the Grim Reaper did not fear the gods, it did not want to wage war against them for no reason.
Cornered and left without a choice, the Fallen Angels then chose the Abyss, and it took them nearly a hundred years to establish a foothold there. To become part of the Abyss Royal Family, it took another near hundred years; at that time, the Abyss was brimming with mighty individuals.
There were even Demon Gods walking the Abyss, at that time the Magic Dragon clan had not yet vanished without a trace.
No, that's not right.
Now Hell has begun to summon the souls of our Fallen Angel race, could it be... the relationship between Hell and the Divine Realm... has cracks appeared?
No, that's not right either, the relationship between Hell and the Divine Realm was never good to begin with.