On a recent Peter Attia Podcast ( https://peterattiamd.com/jakekushner/ ), Jake Kushner (Diabetic Specialist) says it's mainly because the US Government doesn't mind paying $300 + for Insulin (Medicare/Medicaid), so that's what the drug companies charge. In places like Spain it costs about $20 because that's all the Government will pay.
Even if the US Government gave Medicare to all, they would still (tax payer ultimately) be paying $300 + for a bottle of Insulin that costs $20 USD in Spain. What needs to happen is the US Government should demand a better price which should lower the cost for everyone else.
As an alternative for folks who need Insulin and can't get it, is it possible to go to Canada and buy it for $30 CAD (about $20 USD) a bottle. If you need a prescription just see a doctor there. They won't even charge you for a visit at a walk in clinic typically.