For full transparency, I did not enjoy the work. Dazai is a bit much of a “sad boy” for my standards, and it felt like I was reading a 1930s Japanese boy’s anachronistically hosted Tumblr blog.
However, to answer your question, why do people enjoy listening to King Von? It is not exactly the moral character that people are attracted to, but rather the extreme applications of a human’s negative emotions.
While you might not relate to spinning the block on your opps the way Von does, you might harbor feelings of violence from time to time. While you may not be as suicidal as Dazai, there might be times where you feel tired with your spirit eroded away by life’s misfortunes. During those times, it is satisfying to have some sort of vicarious emotional catharsis.
Goodreads has been a sufficient replacement “trophy” for my underfunded self.