Selection bias. People who see OP's books in the search results and conclude it's a shitty book/something is off/etc are not going to leave a review (on a book

Selection bias. People who see OP's books in the search results and conclude it's a shitty book/something is off/etc are not going to leave a review (on a book they didn't buy) to say so. People who spend $10 and 4hrs of their time are inclined to not want to feel like they just wasted that and so will positively review something to reinforce.