One thing I've noticed about self-published books is that a lot of them look self-published. Often the covers are amateurish and obviously self-made, and I think writers don't do themselves any favours by not going with the best cover they can get. It's not as though it's an expensive thing to buy. A great-looking cover can cost as little as $45.00 from somewhere reputable like Vivid Covers. So, why would anyone not want to give their book the best chance they can?