Why and how are people religious?
1. If people are religious, they usually adopt the religion that is dominant in their family or community. A person inclined to be religious in Turkey is unlikely to become a Hindu or Buddhist. A person inclined to be religious in Savannah, Georgia is unlikely to take up Orthodox Christianity. In each case that would change if family members were part of one of those faiths. Usually, a person has a religious identity chosen by a parent before that person is old enough to make a conscious choice.
2. Some people are genetically more inclined to be religious in some religion than others, and in general, women are more inclined to be religious in some religion than men.
3. Religions thrive when they are preserving a threatened culture, while they wither when they merely reinforce a secure establishment culture.
Hence, the Roman Catholic church thrived in Ireland because it preserved Irish culture against Protestant colonial overlords. The white Evangelical Christian religious movement thrives because it protects a threatened white Southern culture that was defeated in the U.S. Civil War. Black churches in the North, and immigrant churches generally, thrive because they preserve the culture of the place of origin of the migrants.
In contrast, the established churches across Europe, and mainline Protestant churches in the U.S. have seen active involvement collapse because the values espoused and culture associated with these respective churches is the secure establishment culture of the places where they are practiced. Immigrant churches start to wither and consolidate after a few generations as the culture of the descendants of the immigrants is assimilated into the establishment culture.
4. Religion, and superstition more generally, thrives when people's well being depends upon seemingly random forces that they can't control and don't fully understand. This is called the "uncertainty hypothesis" in the literature.
Among people prone to religion and superstition are farmers dependent for their livelihood upon the weather, people at risk of contagious disease they don't understand, auditioning actors, gamblers, and refugees.
People abandon religion and superstition when they feel secure and understand the forces that can impact their lives, if they have access to information that allows them to understand. People take up religion when they are insecure.