I think for books its easier to attribute credit to one person compared to like dozens of actors and extra crew to make a city scene in the movie look populated, or like multiple members of a band. Books are just one person responsible for all of it. If the author is good you support them. Where as, sometimes a movie is good, but then one of those producers/script-writers/actors turns out rotten with bad politics (like bigotry) then your support is kinda of goes towards their royalties and fame. With one person, its much easier to research their politics to support them, and simultaneouly easier to organize a boycott writers for their bigotry.