This way they evoke more emotion, so, more of the unthinking (feeling-based) approval: retweets, reposts, just being remembered. When it's funny, it makes people happier along the way, when it's angry, it may make people also feel anger, but a righteous, just anger.
It's a potent drug which is very hard to stop taking recreationally, and also for a just cause. Not as a poster, but most importantly as a reader.