I agree that Purdue Pharma was probably the most significant factor, maybe enhanced by the relative ease of granular lobbying of private doctors as compared to the challenges it may face in universal healthcare systems. However, I do suspect that the limited rights of most US workers to take sick leave served as one more cultural advantage in favour of Purdue's campaign.

In many countries if a doctor believes you're too sick to work you have a right to take leave until you recover, without risking your job and without expending limited "sick days". In those circumstances the doctor will of course prescribe something for your pain, but as a patient you have no incentive to insist the painkiller is strong enough to allow you to continue working.