We keep renouncing violence in the movies and violence on our streets but it seems like violence is here to stay. I personally feel violence in reality and violence in movies be that on buses or cinemas is the hallmark of the 20th and 21st Century. And I do feel that the violence portrayed in a film on a bus is very dangerous particularly when public safety in pubic areas is at risk from aggression, raids, shootings, stabbings and more.
Perhaps they don't view themselves as a self appointed guardian of the world's morality; they take the view that people are adults and quite capable of making choices and decisions themselves without a nanny watching over them.
Or maybe it's just all about profit; they don't care what is shown, and will provide whatever people want to see.