Where did all these Games Workshop novels come from?

Here's a thing I discovered the other day in my local library - nearly a fifth of the books in the adult science-fiction and fantasy section were Warhammer (40K or Fantasy) novelisations.

That seems like a lot relative to the actual quality of the books - and yes, I have read some of them. But I guess you can explain it by the fact that the library-using demographic skews either young or old, and many a teen cuts their gaming teeth on Games Workshop.

I couldn't find any reportage on this phenomenon, so it might actually be worth looking into, if anyone's reading this.