Purpose of Art & Expressive Therapies in Adlerian Training Programs

Adlerian programs offer art therapy training/education. I'm just wondering why that is, and why other forms of creative therapy are not part of the Adler curriculum.
Wondering why Expressive therapies are used? I've heard an author (Bruce Larson) opine that the unrelenting *Impression* of life's demands would ostensibly lead to *Depression* were it not for the relief provided by personal *Expression*. The value of Expressive Therapies can therefore be represented arithmetically using a sort of credit/debit metaphor (which more accurately quotes Larson): Impression - Expression = Depression. It has been said by others that considering Elation to be the opposite of Depression, then Elation = Expression - Impression, expressing the converse of this effective relationship. This completes this Posting on a Positive note.