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Some people simply troll because they enjoy it, it doesn't need any higher or more complicated goal than that. And as long as they can find people they can successfully troll they will continue that, there is ALWAYS bound to be one or another sucker who falls for it.
Hell, even I do troll sometimes. It gives this nice feeling of fulfillment when you see your prey fall into trap, and that again twists your mouth into this self-satisfied grin just like can be seen on every photo of Steve Jobs.