Here is a good resource on it [1]. My understanding is that Purdue pushed hard for marketing, including paying doctors to market for them. This paragraph sums up most of it.
> “Purdue admitted that it marketed and sold its dangerous opioid products to healthcare providers, even though it had reason to believe those providers were diverting them to abusers,” said Rachael A. Honig, First Assistant U.S. Attorney for the District of New Jersey. “The company lied to the Drug Enforcement Administration about steps it had taken to prevent such diversion, fraudulently increasing the amount of its products it was permitted to sell. Purdue also paid kickbacks to providers to encourage them to prescribe even more of its products.”
Is purdue solely at fault here? Absolutely not. Does it seem that Purdue likely knew what was happening, but put profits above public health? In my opinion, yes.
[1] - https://www.justice.gov/opa/pr/opioid-manufacturer-purdue-ph...