Why was my theme or idea refused?

Characters, brands, franchises and artists belong to their owners, and KDP removes books that use them. The studio refuses them before anything is sent to your image engine, with a message like: "“pikachu” belongs to someone else (a character, brand or artist): choose a theme of your own." (or "describe a subject of your own." for a page idea). Planned ideas that name one are left out. Ordinary words are not blocked, and old fairy tales belong to everyone.