Doctors are much more afraid of being sued for giving "too strong" of a pain medication than they are of patients being angry over being left in pain after a major surgery. I've never heard of an opium addict suing the doctor who originally precribed them, but if that hasn't happened, it's only because the plaintiff's attorneys haven't thought of it yet.
No doubt they have to make special reports with giving opiods, and feel that they can only give them to so many patients without raising a red flag. So they "save" their opportunities for those patients that they judge should get them, based on whatever criteria they wish.
The real problem is no oversight, except by doctors themselves. Certain aspects of the medical profession are abhorent to the most of the public, but there is no one to turn to but medical boards who are obsessed with "best practices," which inevitibly come from the branches of medicine who commit what amounts to crimes under the guise of medical treatment.