From the article:
It may sound like a strange juxtaposition: hardened, tattooed offenders donning the cloaks of fantasy characters. Yet both former inmates and correctional officers agree: D&D is more common in prison than you might imagine. Most facilities have at least one game going. Some have a player in every cell block. According to Micah Davis, a former inmate and Dungeon Master imprisoned in Texas, "We had our own table in the dayroom. That's saying something. Aryan brotherhood table, Mexican mafia table, black guy table, and D&D table."
Some of the players are lifelong gamers, who would be doing the same thing if they were on the outside. Others hadn't even heard of D&D until getting locked up. But faced with a dearth of creative outlets, donning a metaphorical robe and wizard hat quickly became a welcome diversion.