Comics and writers across the world revel in the underbelly of what is offensive and what might cause controversy. For instance, one person's black humor might be another person's cheap attempt at trying to make you laugh. The beauty of this is that every movie gets a different reaction. Some people love it, some people hate it, but that doesn't stop it from being there.
Of course, there are occasions where writers might go over the limit, pushing the boundaries that then go on to offend millions of people all in the name of "art". But isn't that just a reflection of the world that we live in? After all, the human race prides itself on freedom of speech. Black comedies aren't successful simply because they are offensive - their appeal runs way deeper than that: they skewer acceptability, playing with offense but never seeking to offer empty provocative.
Sometimes, that outrageousness proves too much for mainstream audiences, but the lack of box office isn't always an indication of a lack of quality. Because there have been some seriously good black comedies over the years.