Why is so little understood about the subconscious?

[wstein]

Because most scientists think the conscious mind IS the brain. The conscious assumes it is the person and thus asks all the wrong questions.

This is most clearly seen on the experiments to test free will. There are brain signals that appear before the conscious mind is aware of there being a choice. Thus scientists assume there is no free will (as the outcome was determined before the conscious mind acted). If they realized the subconscious is part of the mind and self, they would not reach such a faulty conclusion.

[Antares]

Yes, that makes lots of sense. However, according to the common belief, it is not just a one-directional relation, there is also the opposite situation possible: the conscious affecting (programming, directing, guiding...) the sub/un-conscious.