It’s not that the cover art is bad, its just not super flashy like a lot of the big popular books are which make make readers pass over it at first glance. Many of my most favorite series have covers like yours, such as Thaumatology and Aneka Jansen series by Niall Teasdale. He makes a lot of artwork for his books featuring the various characters which, as one of his avid readers now, makes it more enjoyable. The only downfall is that I passed over Niall’s books for about 6 months before I realized how much I liked his work.
My opinion is to keep up the cover and other graphics on the website but redesign the cover on Amazon for sales… Like putting better bait on the fishing hook.