I don't get it. It's reasonable for Mickey mouse's trademark to be evergreen -- nobody could put steamboat willy to represent their own company, but how exactl

I don't get it. It's reasonable for Mickey mouse's trademark to be evergreen -- nobody could put steamboat willy to represent their own company, but how exactly playing a 90 second clip of steamboat willy in a beyond fair use setting (showing a bootleg copy to some friends e.g.) hurts Disney I don't get.