This is a question I am often asked by people in general. As can be seen from the below IACP video the reasons that bring people to train as a therapist are varied and tend to come on the back of previous work & life experiences.
Of course there are also those who work in the counselling/psychotherapy profession directly from training as psychologists having undergraduate and doctorate level training that can take nearly a decade.
Also see a second video below where IACP accredited therapists explain what they feel are the best things about the work of being a therapist.