To generate outrage over drug prices, it’s hard to beat the example of insulin. This life-saving drug is 100 years old this year, but the list prices of insulin products have doubled between 2012 and 2019 and continue to rise. Patients with diabetes are facing an affordability crisis, and some have died trying to stretch their supplies.

Policymakers and the public typically focus on drug manufacturers as the source of the problem. However, our research shows that between 2014 and 2018, the net price received by manufacturers…