When you read a book, you make an economic decision about how to spend your time and money. Life is too short to waste on a book that may disappoint, so before the decision to read and/or buy, a book goes through your filter, which is informed by taste, experience, word of mouth, etc.
The cover is part of this evaluation. The cover conveys information about the book's genre, style, characters, and story. If the cover looks unprofessional, or if the copy on the back doesn't grab you, it's wise and necessary to give the book a pass and look for something more appealing to you.
This isn't "judging a book by its cover," as the oft-misused aphorism goes; that implies a book sucks because the cover sucks. You've simply chosen not to read it, just like you choose what movies to see, or what to eat, or what to wear, or who to ask out on a date. Discernment is an elemental part of life. If you don't filter books this way, you'll find yourself reading a lot of books you don't like.
Only someone who's read a book can judge it. That's why it's important to have an appealing cover, to get through readers' filters so they can be in a position to judge it, good or ill.
As always, let me know what you think in the comments. I'll reply as soon as I can.
I designed the cover art of Seeds of Calamity in Inkscape. Does it pass your filter? If so, I invite you to read the first 4 chapters or get yourself a copy at Amazon.
For a free digital copy of my debut book, Tendrils to the Moon, sign up for the mailing list on the right side of the blog page. Or, if you're viewing the mobile site, click here.