As someone that just published a book through that process, they don't actually care about the content or what it is that your book is about. They're just reviewing it to make sure that there aren't any glaring formatting errors that will cause it to print poorly or make their final product look bad.

They check the DPIs of images, margins, and technical things like that. Absolutely no regard is given for content, and this, IMHO, is exactly how it should be. Self-publishing empowers authors. Sometimes we get junk like 50 Shades of Grey and other times we get gems like The Martian.