A major part of marketing is segmentation. Instead of a shotgun approach and trying to be all things to everyone, marketing companies realised during the 20th century that it was smarter to figure out exactly what type of person would like the particular product and focus on them. Any extras they can pick up is a bonus.
Under the umbrella of Christian, there are many segments of Christian religions, mostly similar but different products. Just like Mercedes makes different model cars that appeal to different people. All made by Mercedes but suited for different purposes.
The WT probably worked out many years ago that their brand isn't for everyone, but that's ok, as long as they focus on the ones they have and capture their children too.
This is exactly what companies do. Someone like Lego brands themselves as a cradle to the grave company, that is Lego is used by consumers from babies to old age. Loyalty to football teams is passed from parents to children. The list goes on.