People repeat behaviour that leads to flooding their brains with pleasurable chemicals. The short-term reward loop acts over hours to years, and the long-term reproductive success loop over generations.
Could people be trained to be less gullible? Or are you as stuck with gullibility as you are with skin colour?
People can undergo a sudden change of thinking and loyalties under threat of death or intense social pressure and isolation from friends and family.
Some people recovering from drugs or alcohol stay with the programs indefinitely, making the recovery program their family, a long-term source of attention rewards.
People under the influence of cults is similar to that we observe in addicts. Typical behaviour for both includes draining bank accounts, neglecting children, destroying relations with family and losing interest in anything except the drug or cult.