My understanding it that they are out of patent, but regulations make it hard for new players to enter the market. Since the number of companies making them are so limited, even the generics cost a lot.
For example, Basaglar is a "generic" of Lantus, but it's still expensive.
Here’s How to Save on Basaglar, the Expensive Lantus “Generic”
https://www.goodrx.com/blog/basaglar-expensive-lantus-generi...
> Basaglar contains the same kind of insulin as Lantus (insulin glargine), and while it is cheaper—Basaglar costs about 15% less than Lantus—it is still expensive, with a cash price of around $450 for a 30-day supply.
Unlike normal generics, the bio-similars need to go through their own clinical trials and prove they work the same as the original. They can't just "use the same ingredients" and release it. Mind you, that doesn't explain the extreme price markup, but it does explain why these "generics" don't follow the same "85% cost reduction" of normal generics. They still have, effectively, a costly R&D phase.
At least, that's my understanding.