Probably because they're just more likely to go see a therapist in the first place.
Discussion
...and financially-sucessful therapists cultivate their insecurities, solipsism and narcissism while maintaining a co-dependent relationship we describe as a "therapuetic relationship".
Causality is not unidirectional there at all.
That implies the therapist is hostile to the patient's mental health. It would be a direct contradiction of the Hippocratic Oath. I highly doubt what you're suggesting is commonplace.