Statisitically speaking, OT practice has significantly diminished within the mental health field since OT was founded a century ago. OT began as a practice almost exclusively focused on mental health, even its roots can be traced to the moral treatment movement ushered in by the physician Pinel in France and the Quaker Tuke in England. Only about 2% of OT's specialize in this area of practice today. While it is so that OT's are somewhat prepared to practice in mental health, it is a relatively under represented area of expertise for a number of reasons.
OT practice has been a very fluid and oportunistic realm. With the physical disabilities of soldiers in WW I & II came a greater focus on phys dis. With the establishment of medicare in the mid sixties, which officially recognized OT in geriatric practice, more OT's entered treatment of older adults. With the establishment of the Individuals with Disabilities in Eduacation Act (IDEA) there came a migration of OT's into pediatric practice. Each of these opportunities came with funding and employment that made it possible for OT's to specialize in one of these areas.
While these developments occured, employment opportunities for OT's in state funded mental health settings began to drop as states began to reduce the population of institutions that focused on mental health. This drop in state funding precipitated a commensurate drop in OT mental health practitioners to about 2% of the field. Meanwhile, the practice of mental health by Psychologists, MFT's, & LCSW's began to solidify and expand into areas once the purview of OT's. Art Therapy, for example, is a specialty within the MFT field. Each of the aforementioned mental health practitioners has a much stronger professional organization than OT's and has protected its turf in statutory skirmishes at the state and federal levels. At the same time, OT's were not officially recognized through licensing procedures in all 50 states until 2014! In a nutshell, while OT was busy expanding beyond its initial specialty of OT, other specialties suplanted OT as a primary mental health provider. This is best exemplified by the fact that the ACA requires mental health coverage to be provided to all those with insurance under Obamacare, but OT's are not considered primary mental health care providers like PsyD's , MFT's, or LCSW's.
This is a complex and complicated inquiry. The bottom line is OT's practice in mental health at the pleasure of those practioners who diagnose mental health clients and refer them for OT. As long as Psychologists, Psychaiatrists, MFT's, & LCSW's recognize and value the contribution occupational therapy in the treatment of those diagnosed with mental health conditions, there will be a place for OT in mental health. It is up to occupational therapists and their professional organizations to promote and make visible the contribution and efficacy of OT in the practice of mental health so its role in this field can expand beyond its current level.