Inspiring art is a benchmark for a quality product in the RPG industry. Without a captivating cover the book relies on marketing and reputation to reach players. For the private publisher this requires budget. Cover-quality art is about $1000 per piece from pro-artists. It will be a gamble if the cover-art alone can net you sales to recoup those costs.
What does this say about the people we sell RPG product to?
They are visually driven. The branding of RPGs is around the imagination of the artist who illustrate the product. It also says, to me, that we gamers are far less imaginative than we believe.
Peace and giggles.