Finding artists willing to participate in any project is very difficult. First they have to be willing to put in the time to get familiar with the style of the universe, then take the time to draw and color it, and then post it in hopes its liked well enough to be included and purchased. Art is a lot of work. So, from an artists perspective, what is a good incentive to show off artwork in hopes it would get chosen for publication?
Also, I've always wondered this, if you commission artwork for a project and the artwork is not what you expected it to turn out like, or it does not fit with the universe or the art style you're looking for, how acceptable is it to ask for them to do it over? I've never encountered this but often wondered what you would do in that situation. Probably the number one reason I haven't commissioned tons of artwork just to get started. I'd like to see it before I pay for it.