IMO because they are old ones, not to say they're past using but i think adding some metaphorical new blood to the franchise would be a good idea, a new setting designed to fit new DnD, the fresh slate that allows them to build things up from the ground, properly cohesively incorporating all the species and classes and such of 5.5 into a greater whole that feels like it fits together rather than have these floating bits of content and lore that feel disconnected from or crowbarred into those existing settings, and doesn't have multiple editions worth of lore buildup to work through for those that want to get into it,