It can make them feel better by giving them a chance to look down on someone else. (The "looking down" doesn't have to be the content of the post - the act of trolling is a form of looking down on someone.)

> It can make them feel better by giving them a chance to look down on someone else.

That's the idea but it does not work. Self esteem is still negative afterwards

Whether or not it works isn't what matters. It's whether or not the perpetrator, consciously or not, believes it works.