In regards to hells dlc, the hells may not be the only place in the DLC that you venture too. But also primarily i believe some lore states that Cyric (the dark sun) is imprisoned somewhere in the hells. So that would be the focus/hook of a dlc in hells. The forge Karlach mentions is a named place in avernus. Abd could easily be a place needed for main story. With or without karlach. Not saying its a garentee but just pointing out its not as unreasonable as some here are saying
