Games Workshop is run by lawyers. They're so bad, they're like a parody of capitalism, but all too real. They constantly attack their fan base for creating fan works, even if it improves their own products.

How do they stay in business then? Well they aren't interested in fan hobbyists. Their product isn't minifigs or rulesets or anything like that. Their product is connecting fathers to sons. Modeling and painting and playing and attending conventions are things that fathers can do with their sons once they age out of that daddy-horsey shit. And Dad's wallet is wide open - how else can he connect with his son, who would otherwise likely spend his time online and due to online influence become completely estranged from his father? That's the product that GW sells, and that's why they can get away with their outrageous attacks on their fans.