The subject of this sentence was us. It uses a subject, verb, and object order to indicate that the speaker is discussing an event or action with one or more other people, and the subject indicates the speaker's action or state. In this case, the subject means that the speaker is us and the verb phrase means to attack or hurt someone or something.
Maybe because they are not the main focus of the original work. For example, if a book has a really strong main character, we might overlook the potential for fanfiction about the secondary characters. Also, lack of promotion. If there is no big fan community actively promoting the fanfiction of these subjects, it's easy to not realize it exists.