There could be several reasons. One reason might be that the novel misrepresents the concept of benediction. Suppose it uses the idea of blessings in a way that is seen as cynical or false. Another reason could be that the novel has some underlying political or social messages that are not welcome. Even though it is a benediction novel on the surface, it might be promoting ideas that are not in line with the powers - that - be. Also, it could be that the literary quality of the novel is so poor that it is considered not worthy of being in the mainstream, and thus blacklisted, despite its theme of benediction.
It could be that the ideas presented in the benediction novel are at odds with the dominant ideology or moral code of a certain group or institution. For example, if the novel's view of blessings or positive elements is too radical or goes against the traditional understanding, it might be blacklisted. Another possibility is that the author has some personal issues or has been associated with something unacceptable, and as a result, the novel gets blacklisted even though it is a benediction novel.