I sometimes wonder whether the BPS psychs found patients with actual psychiatric illness too hard to deal with, so opted for the 'softer' option of specialising in people who were not mentally ill but had difficult to diagnose physical illnesses that they could lazily lump together as psychosomatic. And by definition, a psychosomatic illness, not being real, doesn't require any in-depth research or hard science.
People with ME, being otherwise neglected by doctors, were probably mostly polite and grateful for some attention, which flattered the psych's egos. But also being so worn down by physical exhaustion and malaise that they had no energy to do anything but comply quietly with whatever nonsense the psychs inflicted on them (or pretended to do so), and were too ill with relapses to keep coming back, so they could sign them off as 'cured'.
Throw in a good sprinkling of patients with temporary post viral fatigue who would get better anyway, and stressed people with burn out who would recover with a bit of rationalisation of activities, and you have lots of wonderful 'cures' and grateful patients.
In fact the perfect patient population for lazy psychiatrists with ambitions for power and prestige. Throw in a few imaginary threats and you get the added bonus of being a hero too.