Many of these stock collage covers really have little to do with the actual story inside them. They're great for evoking a vague feel or telegraphing a genre, and cheapskate publishers will try to get the most out of their stock photos.
So, we have embarrassing cover fails like these.
But as Alessandra pointed out, decent painters aren't as expensive as people think. We might not all be Mike Whelan or Kinuko Craft, but DeviantArt has some spiffy designers working for very reasonable prices.
Who might actually READ the damned story and come up with something to showcase it.
And frankly, as a writer, I think covers are super-important. I've not bothered to query three publishers, including one run by a friend, because their covers are truly horrible random collages of stock and out-of-copyright images.