The reason is that the journaling is in part an accumulative method: There is a long period of low-structured input which benefits manifest first acutely (writing in itself seems to be healing through understanding). After you amassed a time-line of thoughts you can try to find throughlines and patterns which then gives you access to deep insights if you have the right tools. Most of the time people use psychologists which I think is in a similar way problematic that people use physical therapists for too much of their problems: Many problems are best solved by the person that has immediate access to the ego-perspective (phenomenological layer, subjective access, etc.) of the problem. This is of course dependent on self-education on basic concepts of what I call true self-care. Self-care seems to be associated with stuff like doing pleasant things (hot bath, nice walks in the sun) nowadays. If you take the antifragile nature of us humans into account this is just another way of the modern hedonist to keep stuck. (This is important for my approach to incorporate journaling into the Zettelkasten Method)