You do understand that opiates are incredibly addicting, right? Everyone's minds are different and some get no withdrawals when they get off their pain meds but there are others where those opiates click and they need to be able to wean off of them just like a lot of other medications out there.
Many people are not informed of the dangers of the medications and the withdrawals they can have from them. I've seen it happen many times before, even with people that haven't touched any type of drug in their life.
It has zero to do with them being weak, you obviously have no idea how drugs and the mind work.