i think the door to hell opn on the fringes of hell so as the colonization is only on his second year and the big guys not even know what is happening . or maybe there is no big bosses at all ....
Lucifer is here, but he's still Samael. Some Arch-Devils are mentionned, they are working for their own sake. There was no reason for them to do otherwise at the beginning, and for the moment the Angels, Fallens or not, are the only one willing to preserve the whole hell.
But when settlers will reach the center, there'll probably meet the one who's ruling the City of Dis and his lieutenants. And I'm pretty sure he'll be smarter than the other, and far better prepared to welcome the visitors...