The mismatch between the awesome artwork and the in-game graphics is... something.
"Hey, we'd love to make a game set in your grimdark universe!"
also
"We think it works best with World of Warcraft-type graphics and cartoon cutscenes!"
But isn't almost every WH40k game like this? Grimdark black and white artwork is what got me into Warhammer back in early 00s and i raged at Dawn of War for basically animating miniatures (that are designed to stand out on the table and be easy to paint) instead of artworks.