Adopt the Missionary Position

How exactly do evil cults recruit followers? There’s typically no shortage of cultists, who throw themselves in the path of adventurers. But how are they converted to a nihilistic or inherently evil faith? When the presence of gods is almost factual, how do you convince someone to abandon a formal church to worship a demon prince? What makes someone turn from the goddess of sunshine and puppies and decide to pray to an unspeakable lord of pestilence?

I’m not sure I have any great answers for these questions. And, really, filling out the backstory of cultists and making them reasonable human beings driven to faith in pure evil just makes the villains sympathetic. It humanizes what should really amount to cannon fodder.