Oh, you think the people actually buy his work because they want to play Warhammer? Nononono. For most people the hobby isn't actually tabletop gaming any more; the hobby itself is actually sitting around and hating Matt Ward and his writing.
Whenever a Battle Sister or a Grey Knight miniature breaks, he gains strength to appear in the material world.
In the long run, we're just a particularly vocal minority. We dislike much of Ward's fluff (albeit he is a good crunch writer when it doesn't come to Daemons), but the legions of preteen kids that get their parents to buy them Ultramarine boxes do very much like it. Which means cash for GW. Which means a happier GW. Also keep in mind that GW itself is hated by much of the fanbase, not to the least because of their rather . . . original . . . pricing policies and their support for fan projects such as Damnatus.