As others have said it's the drug company itself, not an insurance company. The patent they had on the injector has expired so others have tried and failed to bring alternatives to market. Unlike drugs, each medical device has to be vetted by the FDA. Generic drugs can get quicker to market just by showing that they're equivalent to the already approved drug. Devices can't do that.

One of the alternatives was potentially better as they had additional features, but there were problems with the injector itself and it was recalled. That's what other companies have to contend with. It's bad if the injector fails to deliver the dosage and a person dies.

So, people making a 3D printed alternative can't really ensure that the injector works reliably without a lot of work.