I do think there's a mental/psychological component for some sufferers, for sure. Recovery can be incredibly hard. For me, coming off of benefits and taking a huge gamble trying to work again was tough. I didn't know if I'd relapse and end up much worse off - I know a friend with ME doesn't want to 'get better' as the benefits and life she's created suits her now. It's such a part of her identity.
I also 100% believe there are many individuals who suffer with ME/CFS who are desperate to get better and the medical profession are letting them down. Symptoms are not believed or they're diminished, it's not very well understood, and I think ME/CFS is used as a diagnosis when GPS are at a loss as to explaining symptoms. It's this big umbrella term and SO much more research is needed. I do wonder if a percentage of those diagnosed with ME actually have something else going on, as a primary illness, but diagnosing ME stops further investigation.
It's complicated - some I've known have said it's an autoimmune disorder, others say it's a long term viral illness. I don't think ME/CFS is the same for anyone, with varying degrees of severity.
It's not an illness that's in someone's head - I was bedbound for years and my symptoms were very real. But I think I'm trying to say that some sufferers become locked, almost, and no wonder really - it's a debilitating illness and once you've relapsed/pushed yourself a hundred times, it can be tough to get the mental power to keep going.
I was lucky, the right diet/supplements/mental attitude/environment combined so I could recover. It's not just one thing, but a complex set of situations. But I do remember reaching a point and thinking right, I have got to do this, otherwise I'll have no life. Of course I didn't will myself better, it didn't happen overnight, but I used that will to make a lot of changes that in time did lead to my recovery.
I hope that makes sense! I'm certainly not enforcing the negative myth of 'yuppy flu' or 'just try harder' but I also acknowledge how your mental health and outlook can hold you back - for some sufferers. No one has the same experience/trigger/recovery route, as such.