Do you remember when Aranessa was revealed as a part of the Vampire Coast DLC? It made very little sense, even less than marked characters not being part of their god's race. At the time, CA told us they couldn't make that a Dreadfleet DLC, which probably meant that GW would have asked more money for an additional license. So they had to make up a character and add a completely unrelated one to fill the pack.
The bottom line is: some decisions aren't driven by gameplay or lore reasons, but by economical-logistical ones. And that's probably the case with this Chaos DLC. But obviously they couldn't tell us the naked truth. A shame, but in the end this is a for-profit endeavor, not an artistic one.