Some of the best self-published books end up with amateur covers. While professional publishers consider every detail of book’s cover, like whether a font should be sans-serif or not base on genre, independent authors lack the experience to do the same. The Airship explains the process:
All of this, every aspect, from font selection to colors to composition, is put together by a team consisting of representatives from the publisher, editors, the art department, the designer(s), sales and the authors themselves, whose contracts usually stipulate cover design consultation or approval. The whole thing is very much a design-by-committee process.