"Prejudice" implies a passive attitude or belief. Once prejudicial attitudes transform into something actionable or behavioral, they become bigotry or discrimination -- the very essence of an "-ism."

Obviously, the systemic manifestations of any form of bigotry deserve their own (sub?)category, because they will require different solutions. The solutions we apply to combat discrimination in workplaces or educational settings are naturally going to be different than how we confront active bigotry ("-isms") in our daily lives.