Cheap and easy controlled substances are a manufacturer’s dream. It’s expensive because we have a captive healthcare system and they can do whatever they want.

The cheap old varieties of insulin are still available and still cheap. What's expensive are the newer analogues which make it much easier for diabetics to manage their insulin levels.

Thanks for explaining. I wasn’t aware that there were newer insulins with different absorption properties.

The same way that epipen got so expensive:

Executives wanted a larger bonus while lacking the ability to otherwise meet unreasonable “infinite growth” demands of the market.

Supply and demand. If you're going to die without insulin then your demand is fairly inelastic to price changes. If the producer doubles the price, then you'll pay it.

Government regulations. It's as easy as allowing to import it from cross the border from Mexico and Canada.