I think parenting styles emanate from their own personality, and part of it is from their own childhood experiences. Also, it depends on the church they attend, because many churches of various religions give advice on how you should raise your child. Also, it's the cultural norms of the community they live in and/or grew up in that influences their parenting style. It helps a lot if they read parenting books, though. But the way they will follow the book's advice will also be tweaked to what their personal understanding of parenting is.