I’m not surprised in the slightest that you really went to the mat for him. You are always such a great champion for him. And That discovery period trying to find the cause? BRUTAL. It can go on for months, with little instant gratification.
Truth is, for those of us who have life long barbers,, there comes a point where you sort of throw your hands up and say “I’ve done everything I can, this is probably engrained unfixable behavior”. At that point, you tend to release the strain and heartbreak of it. So there’s light at the end of our tunnel. For someone just starting that journey, it can feel hopeless.
It must really be heartbreaking to watch your beloved bird pluck or worse, tear his skin repeatedly and trying everything with varying degrees of success. I don't think I could cope with the emotional distress.
I wonder if it's captivity, cages that are too small (most cages are, IMO), not flying enough, boredom, having been hand raised, heartbreak over loss of the first bonded relationship, being rehomed, or a combination of several of these factors that trigger it. Or hormones and sexual frustration, but I don't think wild unpaired parrots are flying around with bald spots because they didn't get to breed that year. Perhaps larger parrots simply shouldn't be kept in captivity outside the best zoos.
I especially admire those who eventually accept that their beautiful bird can still be beautiful and happy but bare skinned. We don't get rid of our children if they aren't perfect, do we? We don't dump our spouses if they lose their thick, luxuriant hair, their trim, youthful bodies, or flawless faces do we? If our dog loses an eye or a limb we still love them and give them forever homes, right? Its so common that maybe potential parrot owners ought to consider the very real possibility that their parrot may become a plucker and not adopt if they can't handle it.
It's the skin tearing pluckers that are most heartbreaking because it can prove life-threatening. Drugs may be the only hope for those unfortunate creatures. Casper, the Goffin's Cockatoo I adopted and rehomed many years ago, is one of them. She's in a very good home but has worn a collar for over 30 years now. The guilt I feel for having failed Casper would eat me alive if I let it.
I'm lucky that budgies very rarely pluck. Cockatiels also rarely pluck and I haven't seen many small conures that pluck either. Perhaps the smallest parrots aren't as sensitive and intellegent as the most frequent pluckers- the Greys, Amazons, Cockatoos and Macaws.