You can thank the chintzy reimbursement schedule that most insurance companies provide, if at all. A lot of stress-induced mental disorders are treated as preexisting conditions, and its an uphill battle to convince them that it's not.
Personally, I don't like coming up with all kinds of new and different labels for disorders that are not quantitatively different in their effects on the patient.
On the flip side, however, I also dislike "umbrella diagnoses" that lumps every instance of childhood psychosocial dysfunction as ADHD or every instance of social anxiety as Autism.
For that matter, how many residual stress disorders are really PTSD?
It's almost like a poker game between providers and insurance companies:
"OK, I'll see your OCD and raise you one MPD!"
"Call."
"I've got a full house: three narcissists and two anal retentives."
"I've got four Queens and a Transgender. I win"
I take it that you’re a practitioner. I’m trying to figure out why your FR login name isn’t BiPolarik...(heh)...