Two main reasons:
- there are few really high quality therapists in existence (see a book called Focusing by Gendlin if you want more info here)
- all humans posses an [unconscious stability program](https://www.quora.com/search?q=homeostasis%20preservation&author=84795924 “www.quora.com”) running in the psyche. The mandate of this program is “don’t let my identity or coping strategies become destabilized” (aka homeostasis preservation). This means that very good therapists are actually a threat to one part of your psyche, because they will introduce uncomfortable and stressful change into the system.
Given #2, even when you do find a good therapist, there is a strong force that causes you to dismiss or discredit them … thus allowing you to quit therapy without every having your “norm” disrupted or destabilized.
And you can tell it’s an emotional (non-rational) process, because (unless you are well trained), you KNOW you have no skills or credibility that should encourage you to judge or measure a professional in field unrelated to your own expertise.
https://www.quora.com/search?q=homeostasis%20preservation&author=84795924