> I wonder if it's patent law that's keeping them secretive

Many insulin forms are no longer patented. Last year patents (at least in Europe) expired from some quick acting insulin variants and as a result insurers here are forcing everyone to cheaper generics. Side effect: Not all have the same solutions, though the insulin is the same. Despite what the insurers say, YMMV if you switch due to different solutions being present.

So I do not think patents on the product is a real issue. Maybe patents on the production method.