Most older expired IP insulin just isn't very convenient to use for most people; it requires more intense participation from the people using it, so you tend to

Most older expired IP insulin just isn't very convenient to use for most people; it requires more intense participation from the people using it, so you tend to get worse results (imagine if you had to actively think about breathing in enough oxygen every single waking hour of your life -- it's exhausting). The longer acting, more specialized insulins are still heavily patented. When insulin takes longer to work, the person using it has to think less about the insulin and actually gets to live their life rather than think about blood sugar all day. Now, if you closed the loop and used older insulins, you'd have good control and less issues since a computer would bear the cognitive load, but glucose control, especially in the outpatient setting, is ridiculously hard. If you think you can solve it though, give it a shot. It's a multi billion dollar market and a lot of lives you can improve.