Julia meant to be the recurring Character
As you know Hellbound was originally going to end with Julia coming out the mattress because the theory that Clive Barker & Co had is Julia would be the figurehead of the films, but due to Pinhead's popularity they decided to make him the recurring character, Claire Higgins made it clear she didn't want to appear in any further sequels.
Looking back it's hard to imagine why they thought Julia would become a horror icon and didn't think horror fans would become attached to Pinhead & the other cenobites, it seems obvious by just looking at them but not to the filmmakers it didn't.