Partly, I think, because we, as a society, have little appreciation of how complex human thought, feelings, behavior, and interactions are. Partly, because the current marketing system doesn't make money by evaluating and collecting together useful knowledge. You can't put everything a person needs to know to cope with life into a one-hour talk show or one computer disk. That is why I am drawing from hundreds of books and citing hundreds more. It is the best our species can do for now.
Money is made by the rapid turnover of books.
Rarely is a good self-help book well advertised for long. Public libraries don't even buy many of these specialized books. Even I, after 25 years of working in this area, have difficulty finding the best book available for a specific problem. The distribution of knowledge to hurting people is very inefficient. We'd rather make profit than help people.