The world of fantasy artwork is competitive and lucrative for those that have a talent of bringing the words of an author to life. Dragons, elves and more are used to create an interest in a book. As much as I like to see art as a pure platform, the truth is that a book cover is a form of marketing. The people that know how to use that end up making the most money.
Purists that try to keep that aspect out of their art won't make it very far in the industry. Writers have the luxury of having a bit more leeway, but we do have to follow certain rules because that's what the audience want. We can't be too abstract or too off the grid without the fear of alienating or boring our audience.
Art is even more specific. They have to figure out how to draw the essence of a 50,000 word story into a single picture and then make it appealing to an audience. I my opinion, the person who paints the cover art is far more impressive than the guy who actually wrote it. He just had to tell a story, the illustrator had to bring it to life.