Unfortunately, your original question has an answer that is hard to articulate. It is much like asking a fish "why does it swim?". It has to for it to survive. In other words, it is setup to do so naturally. That is the same with those who tend to think visually (pictures, movies, x-ray form, etc.). Their brains are set up to do this by their neural connections that they have. Now that does not stop someone who is not set up to think visually naturally from learning to do it, but it can make it harder for them to become that way. They have to retrain their brain to think in a different format than what was first installed. Current neural pathways must change in this process. How to do that can be tricky and depends greatly upon the one who is being taught and what they are trying to learn.