Many of them are former residents of this place. There is a possibility that their... souls are the power source for the entire town, which notably has no power generators of any kind.

Anyone can become a drone, if their will slackens, or if punished for violation of the edicts of the town masters, or simply because those who rule this place wish to be cruel.

Not all dronings are the same, some turn you into homicidal brutes.

I have killed many murder-drones in my time here, as few can match me with bolter or blade. [ There is no pride in his voice as he says this, no braggadocio. He's just telling the truth. ]