People are willing to pay for art because they then get a certain degree of control in the creative process. So long as you only go after free art, you have to make do with whatever is out there already, or somehow find an artist that is willing to create work to your specification for free (which are very few and far between, usually have long wait times, and often are not amazing). Granted, there is plenty of free art out there, but the more specific you go, the less and less there is. Guro is already quite a specific niche, and there are many subcategories within it. People usually have a certain act they like to see depicted, and it can be difficult to find art that perfectly portrays that in a style you like. That's why you then commission an artist; so that you can work with them to create something that exactly fits your taste. For many, that's worth the money.