Why do book proposals get rejected?

We have to be selective for our readers. If we feel that a book author or editor is not qualified in a particular area, if we note plagiarism, if reviews are poor, if a book author or editor has expectations that we cannot meet, if the market is too saturated with competitors, or if the material or concept is outdated, we may reject a book proposal. Your time is extremely valuable, as is ours, so we try to make smart decisions that are mutually beneficial.