I would also argue that the Game itself and the Black Library drive sales a lot. Without a Game or without the Background books there is no reason to stick to sci-fi minis that are not any merchandise.
Kromlech for example does beautiful Ork minis. They do not produce a game. In a world where no wargames exist, Kromlech could not exist as the niche of people buying small minis just for display is even smaller than the wargaming niche.
I also think that rules drive sales A LOT. I would not be surprised if Serpents and Knights are in high demand while Raptors are sitting on the shelves.