Thats because for chaos marines allegance more greatly emphasizes the roll than 'origin' since Chaos Marines break away and form their own warbands all the time with little regard for the legion/chapter/warband they come from. I think the distinctions for Black Crusade should be based first on Chaos allegence, then class, then 'origin'. A book that leaves out the 'big 4,' is one that leaves out the most immediately recognizable parts of chaos for the sake of emphasizing the part that most would care least about. Clearly FFG is driven by a sense of having as much distinction as possible in the core book hence why with Deathwatch they chose Ultras, DA, BA, BT, and SW as opposed to Ravenguard, Iron hands, Imperial Fists, Salamanders for the first book. What you're saying is the equivalent of if only chapters from Codex: Space Marine had been in Deathwatch.

I think the distinctions will be cut differently than how you're proposing. I think the problem with this is that there is so much redundancy and too little established variation that the distinctions are too far and few to build the core game around. With Undivided, you've got the Red Corsairs, Black Legion, Alpha Legion, Night Lords, Word Bearers and their various Cultist associations. Yeah, it would.but starting off with the Undivided material gives a good springboard, like how Deathwatch focused on the 'Big Name' Chapters. wrote:It'd be silly to have a game about Chaos that didn't have stuff for the 4 Chaos Gods.

Warhammer 40k dark heresy chaos cultist