Because I will not buy WH1 and WH2 and all its DLCs again on Epic if WH3 becomes an Epic exclusive. If that ends up happening, I will cease buying any and all CA and TW games where I stand when discovering that news.
Sorry, but this is just the way that I feel about the situation. CA can tell me all they want "We don't plan to", but as we all know, plans change on a dime where business and money is concerned. Everything has a price. Even Loyalty.