Why is it trauma, that fuels so much artistic creativity, and why do public school frown on traumatic expression?

As both an educator and an artist I'm curious as to why trauma has fueled so much creative expression in artists. Speaking for myself and the traumatic experiences in my own life, creating visual often has helped me find words to my feeling and thoughts. Perhaps creating something out of so much pain and confusion is grounding in some therapeutic fashion. I know that there are massive studies of the benefits of art therapy and the necessity for trauma survivors to express their thoughts and feeling. However I don't understand why so many school boards refused to allow students to express their feeling visually. It seems that rather than allowing a student to paint or depict a disturbing picture their work is used against them by counselors and schools alike. Few kids, even those looking for attention are ready to spill their guts to a school counselor. With no safe place to express their feeling where can students turn to express their feelings when there are often no words to put to them?