I assume that trolls try to provoke erratic and disproportionate reactions from others, becoming a part of their own miniature sitcom for their own entertainment. It could be because of a sense of victory upon watching others break down (assuming a zero sum point of view). It could be the viewpoint that trolls are at their own higher level compared to others and understand each other while making fun of the lower levels (a false sense of superiority). Maybe it's a [case of] holding onto their own beliefs and assuming that they needn't change themselves if they disrupt all conversations that may cause harm to their own beliefs. It might be attention seeking or an escape mechanism. It could also be a desire to avoid fitting in with everyone else and remaining separate.
(edit: grammar)
If I recall correctly, there were multiple posts in different communities.