While I don't know the answer to this in-depth I can share some bullet points and of course it depends on what country you are talking about. On top of that it is important to note that there are insulin shortages in various countries.
- one payer healthcare systems
- non-convoluted distribution systems
- depending where cheaper workforce/cheaper to make the insulin
- less stringent regulatory processes
- stronger lobbying groups in the US
- one payer healthcare systems - non-convoluted distribution systems - depending where cheaper workforce/cheaper to make the insulin - less stringent regulatory processes - stronger lobbying groups in the US