Big Pharma is an easy villain to hate (and there's a lot to hate) but why aren't the doctors who prescribed all these drugs being held accountable as well?
Because the doctors were lied to by Big Pharma. they advertised Oxycontin to doctors as a drug that would not create addiction and claimed that is was safe to prescribe in large doses and for ongoing treatment.
Both should be held accountable. Unfortunately people like to identify single villains or problems instead of realizing that there are many bad players. this is the problem with the whole US health system. Pretty much all parties involved (except the patient) make a lot of money but when people look for a solution they always they to find the one root cause. In reality it's hospitals, doctors, insurance companies, pharmaceutical companies and many others that live well off this insane system.
Some are. There's been quite a few stories of doctors who got shut down for running what the news likes to call "pill mills". Most doctors just didn't overprescribe all that much, though.