Little education, less knowledge, big insecurity and extremely bad examples py parents and relatives.

Same as any group, a gang, a cult, a book club - humans generally crave belonging and if they feel a void they will find something to fill it ... or they are born into it

Childhood indoctrination is the main reason, by far, I think. The next biggest reason might be someone is in a tight spot, like on drugs or something, and desperately turns to religion as the only 'higher power' they know.

The alternative is not different.