I wonder why someone would go through the trouble of writing a good book, have it edited, then write the second or third draft, then have it copy edited and reviewed.......and then do a hasty, poorly designed cover.
Hence when I see a cheap or badly done cover ( and lets face it they are obvious), I wonder to myself.
But of course, a bad cover has nothing to do with the quality of the writing inside, which could be positively Proustian. If you like Proust, that is......
On Kindle anyway, I have never found a good book with poor cover art.