I can't speak for the author but I just figured it was to add a shock value to it. I figured it was meant to be disturbing, usually things like rape, incest, murder, etc. are usually to add a shock value when they go into detail about them. I can't really explain the end. Maybe since the guy lost what made him that way he ended up with another thing that he wanted. But the tragedy of it is he never gets what he wanted to use his new penis for in the first place. Well maybe not a tragedy since he was a bad guy throughout a lot of the story. The story has a lot of irony in it though.