My Reasons are as follows:
1. Online books profit by having a brand, particularly if the author is not widely known.
2. Images can serve as a brand.
3. I like the background I have gotten free on Kindle.
4. The background shows up the title and author name whereas many snappy covers are less clear in that department.
5. I do not like spending money on anything I do online.
6. I feel Kindle Books are a world of their own, a world I like, a world I am trying to learn, and my cover is part of that world.
7. I am contrarian and do not believe I would succeed any other way.