Trolls create anger and conflict and conflict drives engagement. But that is as nothing compared to the engagement you get from public spectacles of righteous indignation. Social media breeds a special sort narcissistic positive feedback loop and it turns out a very small amount of validation is all that is required to set people off.
But trolls usually know they're trolls. On the other hand take for example Twitter user Oli London [1]. I can no longer tell parody from sincere in this "influencers" persona, but wow, does it drive engagement. Is this guy ok? There are thousands of accounts cheering him/them and many others on.