I think that the 'jury is still out' on Fibromyalgia.
It seems that when doctors cannot seem to get a direct diagnosis,
they pass the ball to Fibromyalgia. Some docs (esp neuros) don't seem to think that there is such a condition as Fibromyalgia. They think that it's just a 'dumping ground' for a bunch of undiagnosed related conditions.
It is the newer term, rather than say it is 'idiopathic' they can finally have a condition as a cause.
But the 'jury is still out' for some.