This is, admittedly, speculation on my part based on personal experience. Here goes. I'm sure you know this, but I'd like to throw it out there.
If I want to see a my regular GP and talk about mental health, I schedule a regular appointment and pay my co-pay for the visit and for any pharmaceuticals he prescribes.
If I want to see a mental health professional, I have to call my insurance company, describe my problem to someone who is not a mental health professional, have them pre-authorize visits (if they will), find an in-network therapist and complete treatment in the maximum 5 authorized visits per issue.
A system like this drives people to antidepressants.