This occurs to me often reading comments feeds. I think the need to deny psychiatric involvement stems from the issue that, if you were, for argument's sake, to agree that ME is wholly psychiatric, the disparity between fatigue levels and psychological wellbeing would generally bear out that it isn't a straightforward depression. The next most obvious candidate is a somatoform disorder, which carries with it strong connotations of doing it to oneself and therefore also of the ability to undo it with little or purely psych-oriented intervention. I think that anecdote on the web, of patient experience with cynical friends and family, bears this kind of mindset out, and denying psychiatric involvement is a reflexive response to what can devolve into genuine physical threat to CFS/ME patients, if pressurised to undergo inappropriate GET regimens, to the detriment of their health, or worse. So I don't think speech like 'it isn't just depression' or what have you, is always necessarily intended quite as it sounds, though a renaissance of stigmatising phraseology we doubtless have.

I asked a psychiatrist about the state of physiological research into somatoform disorders, and her response was that more research was needed. She also confirmed me in my understanding that there was some good legitimising physiologic research into major depressive disorder, bipolar disorders and more. Though she was unprepared for the questions and doubtless didn't anticipate me anonymously quoting her on Reddit. Based on this, why it might occur to a hypothetical physician to diagnose with a psychiatric disorder that needs more research and invalidates patient experience, with large numbers experiencing manifestly similar symptoms by chance, instead of a yet-to-be-ultimately-classified disease/disorder that needs more research and validates patient experience, with significant overlap pointing potentially to a single disease process, is confounding.