I think you're making a huge presumption there. Yes, he makes a lot of money, but if you read one of his autobiographical works like
On Writing you'll see that money is very far down the list of his motivations. First and foremost he writes because it's what he does, it's almost 'hardwired' into his consciousness. In other words, it's for the sheer love of it.
Why does an 'artist' write? What makes them different from 'popular' writers? I think people have a specific vision of the 'artist' in their heads (swanning around with a cravat and smoking jacket; starving to death in a loft in Paris; unappreciated in their time; ) when someone doesn't fit that vision, we have a break-down of imagination.
Don't get me wrong, I'm not arguing that King is a genius or anything. Writers like Joyce, Hemingway, Fitzgerald, Faulkner, Woolf et al are light-years ahead of him, but still, his work deserves to be called literature just as much as the work of many lesser so-called literary authors.
ZIPPY