> a novelist only writes a vampire book because that's what the market wants

Not exactly. If you're in it for the money, don't be an artist (because it's not very effective). Having established that you're not in it for the money, don't slavishly follow the market, what's the point of that? But respect your audience, of course, and try to get them to part with their money on your terms, which is the fun of the whole thing and why you're not working in real estate instead.