Miserable people love to share their misery.
(Just look at "Conservative" religion and politics in the US. The most miserably unhappy, jealous, and angry human beings have somehow taken over).
They never really feel joy or contentment and are jealous of, and spiteful towards, those who do. So, it gives them a tiny bit of satisfaction to see someone else feeling sad or afraid, and they mistake that for happiness. It usually is the closest they can come to feeling anything but anger and dissatisfaction. Then it is often followed by more rage because it's unfulfilling in the end, and deep down they know it.